2618铝合金的热变形和加工图_黄光胜
铝合金相图精选ppt
11
YINBANG CLAD
Al－Cu相图
•共 晶 相 图
整理 Yinbang Clad Material Co,. Ltd.
12
YINBANG CLAD
具有化合物的组合相图
整理 Yinbang Clad Material Co,. Ltd.
13
YINBANG CLAD
三元相图恒温截面
整理 Yinbang Clad Material Co,. Ltd.
ZL103铝硅铜合金
• ZAlSi5Cu2 未变质处理 白色a固溶体 片条状共晶硅 少量块状初晶硅 黑色骨骼状Mg2Si
亮灰色Al2Cu
浅灰色骨骼状 Al8Mg3SiFeSi6
整理 Yinbang Clad Material Co,. Ltd.
24
YINBANG CLAD
ZL103铝硅铜合金
• ZAlSi5Cu2 变质处理 白色a固溶体 状共晶硅 少量块状初晶硅 黑色骨骼状
及内应力，提高塑性，通常在高温长时间保温
后空冷。
整理 Yinbang Clad Material Co,. Ltd.
33
YINBANG CLAD
彩色金相
未变质处理 砂型铸造铝 合金中的
• CuAl2相 棕色－紫色
－蓝色或浅 绿色
整理 Yinbang Clad Material Co,. Ltd.
34
YINBANG CLAD
2）淬火（固溶处理） 将铝合金加热到固溶线以上保温后
快冷，使第二相来不及析出，得到过饱 和、不稳定的单一固溶体。淬火后铝 合金的强度和硬度不高，具有很好的塑 性。
整理 Yinbang Clad Material Co,. Ltd.
2026铝合金热变形行为的研究
ＨＵＮＡＮ ＮＯＮＦ ＥＲＲ０ＵＳ ＭＥＴ Ｓ ＡＬ
湖 南有 色金 属
３１
・
材
料பைடு நூலகம்
２２ ０ ６铝 合 金热 变 形 行 为 的 研 究
朱剑 军 ， 黄 蓉 ， 文杰 ， 唐 李 剑
（ 南稀土金属材料研 究院， 南 长 沙 湖 湖 摘 ４０２） １ １６
强 度 。 目前 ，０ ６合 金 已 经作 为 下 翼 面 蒙皮 材 料 被 ２２ 应用 到 了空 中客 车公 司 的大型 飞机 Ａ ８ ３ ０上 。
ｌ 试 验 材 料 与方 法
实验材 料 为 ２ ２ 金 ， 于 Ａ —ｃ ０ ６合 属 ｌ ｕ—Ｍｇ —Ｍｎ
—
ｚ 合 金 ， 名 义化 学成 分 （ 量 分数 ） ： ｕ３ ６ ｒ 其 质 为 Ｃ ．％
的影响 。压 缩 试 验 结 束 后 立 即 对 试 样 进 行 水 淬 处
理， 以保 留其 变 形 组 织 。变 形 温 度 为 ３ ０～４ ０ ℃ ， ０ ５
于 ２ ２ 合 金 热变 形行 为 的本 构方 程 ， 曲正 弦 模 型 ０６ 双 已广泛 用 于金 属 材 料 的 热 变形 研 究 中 ， 于许 多 铝 对 合金 也能 准确 地描 述其 流 变应 力 与 变形 温 度 和 应变 速率 的关 系 ， 方程 中材 料 常数 （ ） 度 的高 低 影 响 但 ａ精
合金 激活 能 的计算 。本 文 以 ２ ２ ０ ６合 金 为试 验 材 料 ， 通过对 双 曲正 弦 函 数 的 材 料 常 数 （ ） 用 ａ＝ｐ ｎ ａ采 ／ 和优 化 处 理 两 种 方 法进 行 求 解 ， 能更 精 确 地 得 出 以
《变形铝合金热处理工艺》在全国出版发行
《变形铝合金热处理工艺》在全国出版发行
佚名
【期刊名称】《金属加工：热加工》
【年(卷),期】2012(000)007
【摘要】由王祝堂教授编写的《变形铝合金热处理工艺》一书已由中南大学出版社出版,并在全国发行。
本书是中国学者撰写的首部有关变形铝合金与铝材的实用性热处理方面的专著,是＂十一五＂国家重点图书出版规划项目——中国有色金属丛书之一。
【总页数】1页(P29-29)
【正文语种】中文
【中图分类】TG161
【相关文献】
1.出版发行体制改革步入新阶段——总署举办全国出版发行体制改革培训班
2.形变热处理工艺对2519A铝合金动态变形行为的影响
3.双级形变热处理工艺中
7A55铝合金热变形行为及热加工图4.双级形变热处理工艺中7A55铝合金热变形行为及热加工图5.《热处理工艺学》出版发行
因版权原因，仅展示原文概要，查看原文内容请购买。
2026铝合金热变形行为的研究_朱剑军
-
Q RT
或 Z= A ex p(
) (3)
= A [ sinh(
) ] nexp
-
Q RT
或 Z = A sinh(
)n
( 4)
式( 1) ~ 式( 4) 中, 是流变应力, R 是气体常数, A 、
n1、 、、n 称为材料常数, 特别地, n1、n 可称为硬
化指数, 可称为硬化系数。上述材料常数间一般
图 2 ln - ln 和 ln - 关系图
在一定的应变和应变速率下, 对( 4) 式取自然对
数并求偏导得:
Q= R ln[ sinh( ) ] / ( 1/ T ) ln ln[ sinh( ) ] T
( 7)
由式( 7) 知, 当 Q 与 T 无关时, ln[ sin h( ) ] 与
1/ T 为线性关系, 令式中 K = ln[ sinh ( ) ] / ( 1/ T ) , K 为直线 ln[ sin h( ) ] - 1/ T 的斜率; n 2 为直 线 ln - ln[ sinh ( ) ] 的斜率。取峰值应力和对应的
如下:
( )=
ln[ m / ( m + ln
1) ] +
m
( 12)
当 ( ) < 0 时, 为非稳态流变。 将功率耗散图与失稳图 重叠就可获得加工图。
应用热加工图来分析合金的加工性能不仅可以优化
加工工艺而且可以避免流变不稳定区域。试验 6156
合金在真应变为 0 9 时的加工图如图 5 所示, 其他 应变的加工图 与此类似。图中阴 影区为流 变失稳
RT )
图 3 H = 时 ln - ln[ sin h( H ) ] 、ln[ sinh ( H ) ] - 1 000/ RT 关系图
2024铝合金板材高温拉伸流变行为和微观组织演化研究
2024铝合金板材高温拉伸流变行为和微观组织演化研究赵婷;邓磊;王新云【摘要】目的：研究高温拉伸应力状态下,2024铝合金板材的流变行为和微观组织演化行为。
方法对退火后的2024铝合金板进行等温拉伸试验,得到其应力应变曲线,并通过金相实验测定平均晶粒尺寸。
建立了2024铝合金板材高温拉伸条件下的流变应力本构关系和晶粒尺寸模型。
结果流变应力随温度的升高而减小。
流变应力对应变速率有正的敏感性,随着温度的升高,应变速率敏感系数变大。
变形后的平均晶粒尺寸随Zener-Hollomon参数升高而减小,随应变量的增加先减小后增大。
结论所建立的流变应力本构关系和晶粒尺寸模型,有助于在实际生产过程中优化工艺参数,获得细小晶粒,提高零件性能。
该研究为2024铝合金板材热成形工艺的开发和组织控制奠定了理论基础。
%ABSTRACT:The aim of this work was to study the flow behavior and microstructure evolution of 2024 aluminum alloy sheet during hot tension deformation. The 2024 aluminum alloy sheet was stretched to get the true stress-strain curves when the range of deformation temperature was 300 ℃ ~450 ℃ and the range of strain rate was 0. 001 s-1 ~0. 1 s-1 , after the deformation, metallographic tests were carried out on the deformed samples to determine the average grain size. The flow stress constitutive relationship and grain size model for 2024 aluminum alloy sheet under hot tension condition were estab-lished using the experiment results. The flow behavior decreased with the increase of temperature. The flow behavior had a positive sensitivity to the strain rate. With the increase of temperature, the sensitivity coefficient of strain rate became lar-ger. After deformation, the average grain size decreased withthe increase of Zener-Hollomon parameter. With the increase of strain, the average grain size first decreased and then increased. The flow stress constitutive relationship and grain size model established were conductive to optimize the process parameters, obtain fine grains and improve the performance of parts in the process of actual production. This study provided a theoretical basis for the development of hot forming process and control of microstructure of 2024 aluminum alloy sheet.【期刊名称】《精密成形工程》【年(卷),期】2015(000)003【总页数】6页(P37-42)【关键词】2024铝合金;热拉伸;流变行为;微观组织演化;平均晶粒尺寸模型【作者】赵婷;邓磊;王新云【作者单位】华中科技大学，武汉430074;华中科技大学，武汉430074;华中科技大学，武汉430074【正文语种】中文【中图分类】TG113.262024铝合金是典型的Al-Cu-Mg系高强度硬铝合金，由于其具有比强度高、焊接性能良好的特点，广泛应用于航天、航空和汽车制造领域［1］。
铝合金热处理
淬火转移时间/s
3 10 20 30 40 60
抗拉强度sh/MPa
533 525 517 460 427 404
屈服强度s0.2/MPa
503 485 461 385 354 316
伸长率δ/%
11.2 10.7 10.3 12.0 11.6 11.0
2024/3/13
淬火
铸铝的淬火冷却介质一般选用热水，以减少铸件的 变形。 对于形状复杂、容易产生变形和裂纹的铸件，以及 要求尺寸稳定性好的铸件，应当在沸水中或热油中 淬火。 铸件形状比较复杂、壁厚相差较大，加热及冷却时 容易发生变形且较难校正，因此加热和淬火速度需 适当减缓。
在空气炉内进行高温加热，如炉膛内湿度 较大或含有其他有害物质，如硫化物，将 加剧铝制品的高温氧化。 特征：在金属表面形成气泡或在金属内形 成空洞。
2024/3/13
淬火（固溶处理）
将铝合金加热到固溶线以上保温一 段时间，使铝合金中的强化相溶入基体， 随后快冷，以抑制强化相在冷却过程中 重新析出，从而获得一种过饱和的以铝 为基的固溶体。淬火后铝合金的强度和 硬度不高，具有很好的塑性。
2024/3/13
淬火工艺参数
加热温度：在避免发生过烧的情况下，尽可能提高 加热温度，促使更多的强化相溶入基体。 保温时间：对于含铜及含镁量高的合金，以及砂型 铸造的厚大铸件，应选取较长的淬火加热保温时间。 转移时间：越短越好。
加热：一般都是加热到相变温度以上，以获得高温 组织。
保温：使内外温度一致，保证显微组织转变完全。
冷却：随炉冷、空冷、水冷。
温度（℃）
L+α
L
α
α+β
Al 水冷
空冷
时间（t） 随炉冷
铝合金热处理工艺
铝合金热处理工艺铝合金热处理原理铝合金铸件的热处理就是选用某一热处理规范，控制加热速度升到某一相应温度下保温一定时间并以一定的速度冷却，改变其合金的组织.其主要目的是提高合金的力学性能，增强耐腐蚀性能，改善加工性能，获得尺寸的稳定性。
铝合金热处理特点众所周知，对于含碳量较高的钢，经淬火后立即获得很高的硬度，而塑性则很低。
然而对铝合金则不然，铝合金刚淬火后，强度与硬度并不会立即升高，至于塑性非但没有下降，反而有所上升。
但这种淬火后的合金，放置一段时间（如4～6昼夜后），强度和硬度会显著提高，而塑性则明显降低。
淬火后铝合金的强度、硬度随时间增长而显著提高的现象，称为时效。
时效可以在常温下发生，称自然时效，也可以在高于室温的某一温度范围（如100～200℃）内发生，称人工时效。
铝合金时效强化原理铝合金的时效硬化是一个相当复杂的过程，它不仅决定于合金的组成、时效工艺，还取决于合金在生产过程中萎缩造成的缺陷，特别是空位、位错的数量和分布等。
目前普遍认为时效硬化是溶质原子偏聚形成硬化区的结果。
铝合金在淬火加热时，合金中形成了空位，在淬火时，由于冷却快，这些空位来不及移出，便被“固定”在晶体内。
这些在过饱和固溶体内的空位大多与溶质原子结合在一起。
由于过饱和固溶体处于不稳定状态，必然向平衡状态转变，空位的存在，加速了溶质原子的扩散速度，因而加速了溶质原子的偏聚。
硬化区的大小和数量取决于淬火温度与淬火冷却速度。
淬火温度越高，空位浓度越大，硬化区的数量也就越多，硬化区的尺寸减小。
淬火冷却速度越大，固溶体内所固定的空位越多，有利于增加硬化区的数量，减小硬化区的尺寸。
沉淀硬化合金系的一个基本特征是随温度而变化的平衡固溶度，即随温度增加固溶度增加，大多数可热处理强化的的铝合金都符合这一条件。
在时效热处理过程中，该合金组织有以下几个变化过程：形成溶质原子偏聚区－G·P（Ⅰ）区。
在新淬火状态的过饱和固溶体中，铜原子在铝晶格中的分布是任意的、无序的。
金属热处理铝合金的热处理课件
铝合金的时效处理
时效处理是铝合金热处理的另一个重要环节 ，通过在室温或低温下长时间放置，使过饱 和固溶体发生分解，形成弥散分布的强化相 ，进一步提高材料的强度和硬度。
时效处理过程中，过饱和固溶体在室温或低 温下长时间放置，会发生分解。随着时间的 推移，强化相逐渐从过饱和固溶体中析出， 形成弥散分布的状态。这种弥散分布的强化 相可以有效地阻碍位错运动，提高材料的强 度和硬度。时效处理是铝合金热处理中不可 或缺的一环，对于提高铝合金的性能具有重
02 铝合金热处理原理
铝合金特性
密度低
铝合金的密度远低于钢铁，具有更好的轻量化 效果。
良好的塑性
铝合金在加工过程中具有良好的塑性，容易形 成各种形状。
良好的导电性和导热性
铝合金具有优良的导电和导热性能，广泛应用于电子和散热器行业。
铝合金热处理原理
加热
01Biblioteka 将铝合金加热到一定温度，使其原子TDM活跃度增加。
加热时间控制
根据铝合金的厚度和热处 理工艺要求，控制加热时 间，确保铝合金材料均匀 受热。
冷却方式选择
根据铝合金的种类和热处 理要求，选择适当的冷却 方式，如风冷、水冷等， 以获得所需的机械性能。
铝合金热处理的质量检测与控制
硬度检测
通过硬度测试，检测铝合金材料的硬度是否达到 要求。
金相组织观察
通过金相显微镜观察，检测铝合金材料的金相组 织是否符合要求。
金属热处理铝合金的热处理课件
• 金属热处理概述 • 铝合金热处理原理 • 铝合金热处理工艺 • 铝合金热处理设备与工艺控制
• 铝合金热处理的发展趋势与未来 展望
• 案例分析：某铝合金产品的热处 理工艺流程
01 金属热处理概述
变形对LF2铝合金高温流变应力的影响
作用增强， 使金属原子热震动的振幅增大， 即原子
间的动能增大， 原子间的临界切应力减弱， 滑移阻
力减小， 新的滑移不断产生， 同时增加了非晶扩散
机理及晶间粘性流动， 使变形阻力降低； ②动态回 复及动态再结晶引起的软化程度也随温度的升高
而增大， 从而减轻或消除由于塑性变形所产生的
加工硬化， 使塑性变形阻力降低， 从而导致合金的 应 力 水 平 降 低［３－５］。
２．２ 应变速率对流变应力的影响 由图 ２ 可看出， 在同一变形温度下， 材料的流
变应力随应变速率的提高而增大。这是因为， 随应
变速率的提高， 单位时间内的应变增加， 位错产 生、运动的数目增大， 位错运动的速度也增大， 加 工硬化的作用更加明显， 从而导致合金变形的临 界 切 应 力 增 大 ， 即 流 变 应 力 增 大 ， 说 明 ＬＦ２ 铝 合 金是正应变速率敏感性材料。
Ｋｅｙ ｗｏｒ ｄｓ： ｆｌｏｗ ｓｔｒｅｓｓ； ｓｔｒａｉｎ ｒａｔｅ； ｄｅｆｏｒｍａｔｉｏｎ ｔｅｍｐｅｒａｔｕｒｅ
在 一 定 的 变 形 温 度 、变 形 程 度 和 变 形 速 度 条 件下的屈服极限， 称为金属的塑性变形阻力或真 应力。金属塑性变形阻力的大小取决于金属的化 学 成 分 、金 属 的 组 织 、变 形 温 度 、 变 形 速 度 、变 形 程度以及与这些有关的各个过程， 如加工硬化、 再 结 晶 、动 态 回 复 等 。 而 变 形 温 度 、变 形 速 度 、变 形程度这三个因素构成金属塑性变形时的热力学 条件 。 ［１－２］ 以往的研究大多是关于高温等温压缩试 验， 得出材料的真应力－ 真应变的关系［３－６］， 本文主要 针对前两个条件对 ＬＦ２ 铝合金进行高温等温拉伸 试验研究， 确定材料的应力应变， 分析应变速率与 变形温度对材料热变形流变应力的影响规律。
铝及铝合金热处理工艺
铝及铝合金热处理工艺(总8页)本页仅作为文档封面，使用时可以删除This document is for reference only-rar21year.March1. 铝及铝合金热处理工艺铝及铝合金热处理的作用将铝及铝合金材料加热到一定的温度并保温一定时间以获得预期的产品组织和性能。
铝及铝合金热处理的主要方法及其基本作用原理 1.2.1 铝及铝合金热处理的分类（见图1）图1 铝及铝合金热处理分类1.2.2 铝及铝合金热处理基本作用原理(1) 退火：产品加热到一定温度并保温到一定时间后以一定的冷却速度冷却到室温。
通过原子扩散、迁移，使之组织更加均匀、稳定、，内应力消除，可大大提高材料的塑性，但强度会降低。
①铸锭均匀化退火：在高温下长期保温，然后以一定速度（高、中、低、慢）冷却，使铸锭化学成分、组织与性能均匀化，可提高材料塑性20%左右，降低挤压力20%左右，提高挤压速度15%左右，同时使材料表面处理质量提高。
②中间退火：又称局部退火或工序间退火，是为了提高材料的塑性，消除材料内部加工应力，在较低的温度下保温较短的时间，以利于续继加工或获得某种性能的组合。
③完全退火：又称成品退火，是在较高温度下，保温一定时间，以获得完全再结晶状态下的软化组织，具有最好的塑性和较低的强度。
(2)固溶淬火处理：将可热处理强化的铝合金材料加热到较高的温度并保持一定的时间，使材料中的第二相或其它可溶成分充分溶解到铝基体中，形成过饱和固溶体，然后以快冷的方法将这种过饱和固溶体保持到室温，它是一种不稳定的状态，因处于高能位状态，溶质原子随时有析出的可能。
但此时材料塑性较高，可进行冷加工或矫直工序。
①在线淬火：对于一些淬火敏感性不高的合金材料，可利用挤压时高温进行固溶，然后用空冷（T5）或用水雾冷却（T6）进行淬火以获得一定的组织和性能。
②离线淬火：对于一些淬火敏感性高的合金材料必须在专门的热处理炉中重新加热到较高的温度并保温一定时间，然后以不大于15秒的转移时间淬入水中或油中，以获得一定的组织和性能，根据设备不同可分为盐浴淬火、空气淬火、立式淬火、卧式淬火。
变形铝合金基础理论――铝的强化方式PPT课件
Cr
Fe
（wt%）
Ni
Ti
极限溶解度
380 ℃ 450℃ 550 ℃ 660℃ 580℃ 660℃ 655℃ 640℃ 665℃
（在一定温度下） 32.8 14.9 5.65 1.82 1.65 0.77 0.052 0.05 1.00
室温下的溶解度
（20℃）
2
＜
＜
2
0.20 0.05 0.05 ≈0 ＜0.1 ＜0.1 ＜0.1
9
三、铝的强化方式
⑴、固溶强化 合金元素加入纯铝中形成铝基固溶体，起固
溶强化作用，使其强度提高。根据合金化的一 般规律，形成无限固溶体或有限固溶体型合金 时，不仅能获得高的强度，而且还能获得优良 的塑性与良好的压力加工性能。
10
三、铝的强化方式
⑴、固溶强化 一般铝的合金化都形成有限固洛体，如Al-Cu、
⑸、冷变形强化 冷变形强化亦称冷作硬化，即金属材料在再
结晶温度以下的冷变形。冷变形后材料即被强 化，强化的程度随变形度、变形温度及材料本 身的性质而不同。
29
三、铝的强化方式
⑸、冷变形强化 同一种材料在同一温度下冷变形时，变形
度越大则强度越高。但塑性随变形程度的增加 而降低。
30
三、铝的强化方式
7
三、铝的强化方式
常见的合金化元素 铝在合金化时常加入的合金元素有铜、镁、
锌、硅、锰、铬、镍、钴、钛及锶等，稀土元 素在某些铝合金中也有适量加入。
8
三、铝的强化方式
常见的强化方法 合金元素元素对铝的强化作用主要通过以下
几方面实现 ： ⑴、固溶强化 ⑵、时效强化 ⑶、过剩相强化 ⑷、细化组织强化及变质处理 ⑸、冷变形强化
16
喷射成形超高强铝合金热变形工艺与组织调控技术
喷射成形超高强铝合金热变形工艺与组织调控技术
喷射成形是一种先进的金属成形工艺，可以制备高性能的铝合金材料。
关于喷射成形超高强铝合金热变形工艺与组织调控技术，其主要涉及以下几个关键方面：
1. 热加工图：通过建立喷射成形超高强铝合金的热加工图，可以确定合适的热加工工艺参数窗口，从而获得良好的成形性能和组织。
热加工图可以采用实验和模拟相结合的方法进行绘制。
2. 热变形行为：研究喷射成形超高强铝合金的热变形行为，包括应力-应变曲线、流动应力、动态再结晶等，有助于理解材料的热变形机制和优化成形工艺。
3. 微观组织调控：通过控制热加工参数和后续处理工艺，可以调控喷射成形超高强铝合金的微观组织，如晶粒尺寸、相组成、第二相分布等。
这些微观组织参数对材料的力学性能和成形性能具有重要影响。
4. 性能优化：通过合理的热变形工艺和组织调控，可以显著提高喷射成形超高强铝合金的力学性能，如强度、韧性、疲劳性能等。
同时，也可以改善其成形性能，使其适用于更广泛的应用领域。
5. 工业应用：喷射成形超高强铝合金在航空航天、汽车、轨道交通等领域具有广阔的应用前景。
通过推广和应用相关热变形工艺与组织调控技术，可以实现喷射成形超高强铝合金的规模化生产和应用。
总之，喷射成形超高强铝合金热变形工艺与组织调控技术是一个涉及多个方面的研究领域。
通过深入研究和优化，有望为高性能铝合金材料的发展和应用提供重要的技术支持。
典型7000系铝合金的热变形行为和加工图
Hot deformation and processing map of a typical Al–Zn–Mg–Cu alloyY.C.Lin a ,b ,⇑,Lei-Ting Li a ,b ,Yu-Chi Xia a ,b ,Yu-Qiang Jiang a ,ba School of Mechanical and Electrical Engineering,Central South University,Changsha 410083,China bState Key Laboratory of High Performance Complex Manufacturing,Changsha 410083,Chinaa r t i c l e i n f o Article history:Received 2August 2012Received in revised form 1October 2012Accepted 22October 2012Available online 2November 2012Keywords:Metals and alloys Microstructure Processing mapa b s t r a c tThe high-temperature flow behavior of 7075aluminum alloy was studied by hot compressive tests.Based on the experimental data,the efficiencies of power dissipation and instability parameter were evaluated.Processing maps were constructed by superimposing the instability map over the power dissipation map.Microstructural evolution of 7075aluminum alloy during the hot compression was analyzed to correlate with the processing maps.It can be found that the flow stresses increase with the increase of strain rate or the decrease of deformation temperature.The high-angle boundaries and coarse precipitations distrib-uting in the grain interior/boundaries,which may result in the deep inter-granular corrosion and large areas of denudation layer,should be avoided in the final products.The optimum hot working domain is the temperature range of 623–723K and strain rate range of 0.001–0.05s À1.Ó2012Elsevier B.V.All rights reserved.1.IntroductionDuring hot forming process,the effects of strain rate and defor-mation temperature on the mechanical properties of metals and al-loys are significant.Generally,there are several types of metallurgical phenomena during the hot deformation,such as the dynamic recrystallization (DRX)[1–7],metadynamic recrystalliza-tion (MDRX)[8–11]and static recrystallization (SDRX)[12–15],which result in the complex microstructural evolution in alloys [16–19].In order to obtain the optimum hot working process,a good understanding of processing map and microstructural evolution is very important for the designers of metal forming processes [20–23].Dynamic material modeling (DMM)aims to correlate the con-stitutive behavior with microstructural evolution,flow instability and hot workability.Based on the dynamic material model (DMM),the processing map was developed by Prasad et al.[24].Processing maps are useful to identify the deformation tempera-ture-strain rate windows for hot working.In recent years,process-ing maps are being developed to optimize the hot working processes of the metals or alloys [25–35].Prasad and Seshachary-ulu [25]found that the stable domains can be related to dynamic recrystallization with high power dissipation efficiency,while the instability domains correlated to the adiabatic shear bands forma-tion.Abbasia and Momeni [26]studied the hot workability of Fe–29Ni–17Co alloy by the mechanical testing and microstructural observations,and established the processing maps for the studied material.Momeni and Dehghani [27,28]characterized the hot deformation behavior of 410martensitic and 2205austenite–ferrite duplex stainless steels using constitutive equations and processing maps.Ramanathan et al.[30]developed the processing map for Al/SiC p composite,and the relationship between micro-structure and hot workability were investigated through micro-structural observations.Samantaray et al.[31]studied the processing parameters of a nitrogen enhanced 316L(N)stainless steel based on the high-temperature flow behavior and microstruc-tural evolution,and the optimum window for the hot deformation were identified as 1350–1423K and 0.001–0.05s À1with peak effi-ciency of 50%and activation energy of 150kJ/mol.Also,Samanta-ray et al.[32,33]optimized the hot working parameters for the modified 9Cr–1Mo (P91)steel by the dynamic materials model.The optimum hot working parameters for Al6063/0.75Al 2O 3/0.75Y 2O 3nano-composite were identified,and the flow instability characteristic were validated by processing maps and micrographs [34].Senthilkumar et al.[35]developed the processing map of the Al based nanocomposite by superimposing the instability map over dissipation efficiency map in the temperature and strain rate space,and different deformation mechanisms such as dynamic recrystal-lization (DRX),dynamic recovery and flow localization were vali-dated by the manifestation of many microstructural features after deformation.Due to its excellent strength/weight ratio,high strength 7075aluminum alloy,a typical Al–Zn–Mg–Cu alloy,is widely used as the aircraft structure components.In the past,the hot deformation behavior of 7075aluminum alloy was investigated by some researchers.Rajamuthamilselvan and Ramanathan [36]studied the hot deformation behavior of stir cast 7075alloy using process-ing maps.Lin et al.[37,38]found that some material parameters are sensitive to the strain rate and deformation temperature.They0925-8388/$-see front matter Ó2012Elsevier B.V.All rights reserved./10.1016/j.jallcom.2012.10.114⇑Corresponding author at:School of Mechanical and Electrical Engineering,Central South University,Changsha 410083,China.Tel.:+86015200817337.E-mail addresses:yclin@ ,linyongcheng@ (Y.C.Lin).developed the modified Johnson–Cook constitutive models to pre-dict the hot compressiveflow behavior of7075aluminum alloy. Despite a number of investigations invested into the behaviors of 7075aluminum alloy,further analysis should be carried out to optimize the hot working process.The objective of this study is to characterize the hot compres-sive deformation behavior of7075aluminum alloy under wide range of the deformation temperature and strain rate.Effects of strain on the efficiency of power dissipation and instability param-eter were investigated.Based on the Dynamic Material Model (DMM),the processing maps of the studied alloy were constructed to optimize the hot working parameters.Besides,microstructures were observed to validate the deformation mechanisms of7075 aluminum alloy.2.Materials and experimentsIn this investigation,the commercial7075aluminum alloy(a typical Al–Zn–Mg–Cu alloy)was used,and its chemical composition(wt.%)is shown in Table1. Cylindrical specimens of10mm in diameter and12mm in height were machined for experiments.Theflat ends of the specimen were recessed to a depth of 0.1mm deep to entrap the lubricant of graphite mixed with machine oil to mini-mize the friction between the specimens and die during the hot deformation.In or-der to study the hot compressive behavior,the hot compression experiments were carried out on Gleeble-1500thermo-simulation machine.Four different deforma-tion temperatures(573,623,673and723K)and four different strain rates (0.001,0.01,0.1and1sÀ1)were used in the experiments.Before the compression tests,the specimens were heated to the deformation temperature at the heating rate of10K/s,and held for3min at isothermal conditions in order to obtain the uni-form deformation temperature.The reduction of the specimen’height was60%and the tested specimens were quenched with water immediately at the end of com-pression tests.The deformed specimens were sliced paralleled to the axial section. The exposed surfaces were polished and etched with Keller’s solution.The optical microstructures were observed on Leica DMIRM image analyzer.Transmission elec-tron microscopy(TEM)analysis was carried out to investigate the precipitate mor-phology and sub-grains of the compressed7075aluminum alloy.The followings are the steps to prepare the thin foil samples for TEM experiments.Firstly,1.0–2.0mm thick foils were cut from the deformed specimens.Then,the thick foils were grin-ded into0.7–0.8mm thin foils.Finally,several disks with3mm in diameter were punched out from these thin foils,and subsequently electro-polished using a solu-tion of HNO3and methanol(1:3in volume).TEM foil examples were examined using a TecnaiG2-20microscope operating at200kV.3.Experimental results and discussion3.1.True strain–true stress curvesThe force-stroke of the specimens during compression tests can be automatically saved by the testing machine,and the experimen-tal data can be easily transformed into the true stress–true strain curves,as shown in Fig.1.Obviously,the effects of the deformation temperature and strain rate on theflow behavior of7075alumi-num alloy are significant.The stress increases sharply until a peak stress at a very small strain.In the following deformation period, the stress decreases until a relatively stable stress appears,show-ing a dynamicflow softening.Generally,the true stress-true strain curves can indicate the intrinsic relationship between theflow stress and thermal-dynamic behavior.During the initial stage of deformation,the work hardening results in the rapid increase of theflow stress.With the increase of the deformation degree,the dislocation density and the potential driving force of recovery in-creases.Meanwhile,the nucleation and growth of new grains oc-curs,i.e.,sub-grains develop.When the work hardening and recovery reach a dynamic equilibrium,the dislocation density re-mains relatively constant and steady stateflow stress is obtainedTable1Chemical compositions of7075aluminum alloy(wt.%).Composition Zn Mg Cu Cr Fe Mn Ti Si Al Content(wt.%) 5.8 2.3 1.50.210.160.050.020.07Bal.Y.C.Lin et al./Journal of Alloys and Compounds550(2013)438–445439[39].So,the softening phenomenon is mainly attributed to the dy-namic recovery(DRV)and continuous dynamic recrystallization (DRX).For the cases with the deformation temperature of573K and all the tested strain rates,theflow stresses rapidly decreases with the further increase of deformation degree after the peak strain(corresponding to the peak stress).This phenomenon may be induced by the high angle grain boundaries forming via the con-tinuous DRX.It takes a little long time for theflow stress and the microstructure to reach a steady state when the material under-goes continuous DRX[40],which results in a relatively quick de-crease of theflow stress.Increasing the strain rate,there is not sufficient time for the growth of the misorientation among the subgrains,leading to the relatively steadyflow stresses.Also,it may indicate that theflow behavior of the material is unstable when the deformation temperature is573K,which will be dis-cussed below.3.2.Establishment of processing map for7075aluminum alloy3.2.1.The principles for processing mapsAccording to the principles of the Dynamic Material Model[24], the materials undergo the hot deformation can be considered as a power dissipater,and the instantaneous power dissipated(P)can be divided into two complementary parts,i.e.,G content(temper-ature rise)and J co-content(microstructure mechanisms),which can be represented as a function offlow stress(r),strain(e)and strain rateð_eÞ:P¼r_e¼GþJ¼Z_er d_eþZ r_e d rð1ÞFor the given strain and deformation temperature,theflow stress can be expressed asr¼K_e mð2Þwhere K is a material constant,m is the strain rate sensitivity used to partition the power into G content and J co-content:m¼d Jd G¼@ðln rÞ@ðln_eÞð3ÞJ co-content can be expressed as,J¼Z r_e d r¼mmþ1r_eð4ÞFor an ideal linear dissipation process,m=1and Jmax¼r_e=2. The power-dissipation capacity of the material can be represented by the efficiency of power dissipation(g),g¼JJmax¼2mmþ1ð5ÞTaking use of the principle of the maximum rate of entropy of production,a continuum criterion for the occurrence offlow instabilities is defined in terms of another dimensionless parameter(n),440Y.C.Lin et al./Journal of Alloys and Compounds550(2013)438–445nð_eÞ¼@lnðmmþ1Þ@ln_eþm60ð6ÞThe values of m can be obtained by differentiating the three order polynomialfitting line of ln_eÀln r plots,as shown in Fig.2.Then, the values of g and n can be calculated by Eqs.(5)and(6).The power dissipation map is constituted by the three-dimen-sional variations of the efficiency of power dissipation with the deformation temperature and strain rate at constant strain,and can be considered as a contour map representing iso-efficiency contours in a deformation temperature–strain rate frame.This map depicts the manner in which the power is dissipated through microstructural changes during the hot deformation,and hence re-veals the domain in which a specific mechanism may become attractive for minimizing the energy of the dissipated state.The three-dimensional variation of the instability parameter(n)with the deformation temperature and strain rate represents the insta-bility map,in which the shade regions with a negative parameter indicate theflow instable domains.A processing map can be con-structed by superimposing the instability map over the power dis-sipation map,from which individual microstructure processes and the limiting conditions for the regimes offlow instability can be obtained.The highest efficiencies of power dissipation do not nec-essarily mean better workability and may be the result of some variations of instability such as wedge crack.So,by processing un-der conditions of highest efficiency in the‘‘safe’’domains and avoiding the regimes offlow instabilities,the intrinsic workability of the material may be optimized and microstructural control may be achieved.3.2.2.Effects of strain on the efficiency of power dissipationFig.3shows the effects of strain on the efficiency of power dis-sipation(g)of7075aluminum alloy under the studied experimen-tal conditions.Obviously,the values of g increase with the increase of strain under the strain rates of0.001sÀ1(Fig.3a)and0.01sÀ1 (Fig.3b),except that there is a decreasing trend under the strain rate of0.001sÀ1and deformation temperature of723K.However,when the strain rate is1sÀ1,the values of g decrease with the in-crease of strain,as shown in Fig.3(d).For the case with strain rate of0.1sÀ1,the effects of strain on the efficiency of power dissipation are not obvious(Fig.3c).The efficiency of power dissipation(g),which is a dimensionless parameter,can be used to indicate the dissipation of power in-duced by the microstructural evolution.Generally,the material shows the good workability when deformed in the domain with the high efficiency of power dissipation.However,the highest effi-ciencies of power dissipation do not necessarily mean better work-ability and may be the result of some variations of instability such as wedge crack.Hence,only the deformation temperature and strain rate corresponding to the peak efficiency in the‘safe’domain of the processing map can be considered as the optimum hot work-ing parameters.3.2.3.Effects of strain on the instability parameterFig.4shows the effects of strain on the instability parameter(n) of7075aluminum alloy under different experimental conditions. Obviously,when the deformation temperature is573K,the values of instability parameter are negative under relatively low strain rates,and the positive values appear with the increase of the strain rate.The negative n values indicate the hot deformation processing in these cases is not‘‘safe’’.This phenomenon may be induced by the high angle grain boundaries forming via the continuous DRX, and theflow behavior of the material is unstable when the defor-mation temperature is573K,as discussed in Section3.1.Increas-ing the strain rate results in the insufficient time for the growth of the misorientation among the subgrains,and the relatively stea-dyflow appears.Also,the increase of strain makes the negative do-mains become more and more large.For example,when the deformation temperatures are623and673K,the values of insta-bility parameter vary from positive to negative(the strain>0.4). The interpretation of these phenomena is based on the fact that the material presents some type of unstableflows manifestation, such as the adiabatic shear bands orflow localization[21].Y.C.Lin et al./Journal of Alloys and Compounds550(2013)438–4454413.2.4.Effects of strain on processing maps and microstructural evolutionFig.5illustrates the effects of strain on the processing maps generated in the temperature range of573–723K and strain rate range of0.001–1sÀ1.The contours in the maps represent the per-centage efficiency of power dissipation.From Fig.5,it can be found that the shaded areas denoting the instability domains increase with the increase of strain.Meanwhile,the shapes of the process-ing maps are similar for the strain ranging from0.1to0.3. However,there exist obvious differences in the shape of the pro-cessing map when the strain is larger than0.3,resulting from the occurrence of the dynamic recrystallization under these working conditions.Fig.6shows the optical microstructures of the de-formed7075aluminum alloy,which indicates that the higher the strain,thefiner the grains.This phenomenon can be well explained by the theory of continuous DRX for alloys with high stacking fault energy(SFE),i.e.,aluminum alloys.The amounts of the stored en-ergy and defects(such as dislocation)within the crystal lattice in-crease with the increase of deformation degree,leading to the sufficient mobility of the dislocations.Additionally,the continuous DRX occurs since the dislocations rearrangement among subgrain boundaries and the misorientation among the adjacent subgrains increase during the hot deformation of7075aluminum alloy.As a result,many subgrains appear,making the low angle grain boundaries transform to high angle grain boundaries.Meanwhile, the grains are refined.Fig.7(a)shows the TEM micrograph of the as-received7075aluminum alloy and exhibits that the sub-grains are equiaxed and relatively large.When the material are deformed under the temperature of673K and the strain rate of0.1sÀ1,some fine sub-grains with high angle grain boundaries appear along the serrated sub-boundaries,as shown in Fig.7(b).It reveals that the original microstructure has been replaced by the recrystallization microstructures.From Fig.5(e),it can be found that there are three typical peak efficiency domains in the processing map.Thefirst domain is the deformation temperature ranging from573K to600K and strain rate ranging up to0.002sÀ1.The maximum efficiency in this do-main is34.4%.This region is not suitable for the bulk metal pro-cessing because this domain is very close to the instable domain and rather narrow.The second domain is the deformation temper-ature ranging from690K to723K and strain rate ranging up to 0.002sÀ1.The efficiency of this domain increases from23%to 29.5%.The third domain is the deformation temperature ranging from710K to723K and strain rate ranging from1sÀ1to 1.995sÀ1with a peak efficiency of32.5%.This stable domain is also close to the instable domain andflow instability may occur if the deformation temperature decreases under a constant strain rate during the hot deformation.The stable domain may correlate with the super-plasticity or dynamic recrystallization.The efficiency of power dissipation for occurrence of super-plasticity is beyond 60%and the peak efficiency for7075aluminum alloy is no higher than32.5%.Therefore,super-plasticity does not occur in these do-mains.Generally,dynamic recrystallization is a beneficial process during the hot deformation because it can produce the stableflow.442Y.C.Lin et al./Journal of Alloys and Compounds550(2013)438–445Thus,the dynamic recrystallization domain is often chosen for optimizing the hot forming process and controlling the microstruc-tures[30].The processing map exhibits that the optimum hot working domains for the reasonable dynamic recrystallization is the temperature range of623–723K and strain rate range of 0.001–0.05sÀ1with a peak efficiency of29.5%.Meanwhile,the shaded domain in Fig.5(e)represents the re-gimes offlow instabilities(e.g.adiabatic shear bands orflow local-ization)under the low deformation temperature and high strain rate.The microstructure in this domain is usually associated with theflow ually,theflow localization occurs before or at the peak loadings.The material may experience the softening or degradation in its load carrying capacity after the peak.But,it still continues to carry the reduced load,while the growth and coa-lescence of micro-cracks continue[30].However,evidences of the flow localization or plastic instability manifestations are not found in this study.There are the high-angle boundaries under the tem-perature of573K and strain rate of0.001sÀ1,as shown in Fig.8. When the strain rate is low,a number of sub-grains grows up, which easily enlarge the angles of grain boundaries.From Fig.8, it can be found that the sub-grains are well deformed with the high-angle boundaries,and coarse precipitations are distributed in the grain interior and boundaries,which may lead to the deep inter-granular corrosion and large areas of denudation layer [41,42].Generally,these high-angle boundaries are not expected to occur in the microstructures of the deformed material.There-fore,the deformation temperatures and strain rates in the instabil-ity domain should be avoided during the hot deformation.4.ConclusionsThe hot compressive behaviors of7075aluminum alloy were studied under wide deformation temperatures and strain rates. Based on the experimental data,the processing maps were con-structed by superposing the instability map over the power dissi-pation map at a series of strains.It can be concluded that,firstly, the deformation temperature and strain rate have a great effect on theflow stress of7075aluminum alloy.Increasing the strain rate or decreasing the deformation temperature can increase the flow stress.Secondly,the effects of strain on the processing map are significant.The values of efficiency of power dissipation in-crease with the increase of strain when the strain rates are 0.001sÀ1and0.01sÀ1.However,the increase of strain decreases the power dissipation values under the strain rate of1sÀ1.For the case with the strain rate of0.1sÀ1,the effects of strain on the power dissipation are not obvious.Thirdly,with the increase of strain,the instability domains in the processing map increase, indicating that some types of unstableflow manifestation(e.g. adiabatic shear bands orflow localization)occur during the hotY.C.Lin et al./Journal of Alloys and Compounds550(2013)438–445443evolution in the deformed specimens with deformation degrees of(a)20%;(b)30%;(c)40%;(d)50%;(e)60%;and(f) TEM micrographs of(a)as-received and(b)deformed specimen under the temperature of673K and strain rate of0.18.TEM micrographs of the specimen deformed under the temperature of573K and strain rate of0.001deformation.Fourthly,the high-angle boundaries and coarse pre-cipitations distributing in the grain interior and boundaries may lead to the deep inter-granular corrosion and large areas of denu-dation layer,and are not expected to occur in the microstructures of the deformed material.Finally,the temperature range of623–723K and strain rate range of0.001–0.05sÀ1can be considered as the optimum hot working parameters.AcknowledgmentsThis work was supported by the Program for New Century Excellent Talents in University(No.NCET-10-0838),Sheng-hua Yu-ying Program,Fundamental Research Funds for the Central Universities of Central South University(2012zzts076),and the Graduate Degree Thesis Innovation Foundation of Central South University(No.2011ssxt094),China.References[1]S.Mandal,P.V.Sivaprasad,R.K.Dube,B.Raj,Mater.Sci.Forum550(2007)601.[2]M.Mirzaee,H.Keshmiri,G.R.Ebrahimi,A.Momeni,Mater.Sci.Eng.A551(2012)25.[3]K.L.Wang,M.W.Fu,S.Q.Lu,X.Li,Mater.Des.32(2011)1283.[4]B.Oberdorfer,E.M.Steyskal,W.Sprengel,R.Pippan,M.Zehetbauer,W.Puff,R.Würschum,J.Alloys Comp.509(2011)309.[5]Z.Zhang,M.Wang,Z.Li,N.Jiang,S.Hao,J.Gong,H.Hu,J.Alloys Comp.509(2011)5571.[6]A.Momeni,K.Dehghani,G.R.Ebrahimi,J.Alloys Comp.509(2011)9387.[7]F.Otto,J.Frenzel,G.Eggeler,J.Alloys Comp.509(2011)4073.[8]F.Chen,Z.S.Cui,D.S.Sui,B.Fu,Mater.Sci.Eng.A540(2012)46.[9]Y.C.Lin,M.S.Chen,J.Zhong,J.Mater.Process.Tech.209(2009)2477.[10]Y.C.Lin,L.T.Li,Y.C.Xia,Comput.Mater.Sci.50(2011)2038.[11]B.Ma,Y.Peng,Y.F.Liu,B.Jia,J.Cent.South Univ.Tech.17(2010)911.[12]M.S.Salehi,S.Serajzadeh,Comput.Mater.Sci.49(2010)773.[13]M.S.Salehi,S.Serajzadeh,Comput.Mater.Sci.53(2012)145.[14]Y.C.Lin,M.S.Chen,J.Mater.Sci.44(2009)835.[15]Y.C.Lin,M.S.Chen,J.Zhong,Comput.Mater.Sci.44(2008)316.[16]K.P.Rao,Y.V.R.K.Prasad,C.Dharmendra,N.Hort,K.U.Kainer,Mater.Sci.Eng.A528(2011)6964.[17]S.Mandal,P.V.Sivaprasad,B.Raj,V.S.Sarma,Metall.Mater.Trans.A39(2008)3298.[18]B.Bradaskja,B.Pirnar,M.Fazarinc,P.Fajfar,Steel Res.Int.82(2011)346.[19]J.Luo,M.Q.Li,Mater.Sci.Eng.A538(2012)156.[20]Y.C.Lin,M.S.Chen,J.Zhong,Comput.Mater.Sci.42(2008)470.[21]Y.C.Lin,G.Liu,Mater.Sci.Eng.A523(2009)139.[22]B.Eghbali,Mater.Sci.Eng.A527(2010)3402.[23]K.P.Rao,Y.V.R.K.Prasad,K.Suresh,Mater.Des.32(2011)4874.[24]Y.V.R.K.Prasad,H.L.Gegel,S.M.Doraivelu,J.C.Malas,J.T.Morgan,rk,D.R.Barker,Metall.Mater.Trans.A15(1984)1883.[25]Y.V.R.K.Prasad,T.Seshacharyulu,Mater.Sci.Eng.A243(1998)82.[26]S.M.Abbasi,A.Momeni,Mater.Sci.Eng.A552(2012)330.[27]A.Momeni,K.Dehghani,Mater.Sci.Eng.A527(2010)5467.[28]A.Momeni,K.Dehghani,Mater.Sci.Eng.A528(2011)1448.[29]S.Ramanathan,R.Karthikeyan,G.Ganasen,Mater.Sci.Eng.A441(2006)321.[30]S.Ramanathan,R.Karthikeyan,M.Gupta,J.Mater.Process.Tech.183(2007)104.[31]D.Samantaray,S.Mandal,V.Kumar,S.K.Albert,A.K.Bhaduri,T.Jayakumar,Mater.Sci.Eng.A552(2012)236.[32]D.Samantaray,S.Mandal,A.K.Bhaduri,Mater.Sci.Eng.A528(2011)5204.[33]D.Samantaray,S.Mandal,A.K.Bhaduri,Mater.Des.32(2011)716.[34]H.Ahamed,V.Senthilkumar,Mater.Sci.Eng.A539(2012)349.[35]V.Senthilkumar,A.Balaji,R.Narayanasamy,Mater.Des.37(2012)102.[36]M.Rajamuthamilselvan,S.Ramanathan,J.Alloys Comp.509(2011)948.[37]Y.C.Lin,L.T.Li,Y.X.Fu,Y.Q.Jiang,J.Mater.Sci.47(2011)1306.[38]Y.C.Lin,L.T.Li,Y.Q.Jiang,Exp.Mech.52(2012)993.[39]D.Samantaray,S.Mandal,C.Phaniraj,A.K.Bhaduri,Mater.Sci.Eng.A528(2011)8565.[40]F.Montheillet,J.P.Thomas,Metall.Mater.High Struct.Effic.146(2004)357.[41]X.H.Chen,K.H.Chen,X.Liang,S.Y.Chen,G.S.Peng,Chinese J.Nonferrous Met.21(2011)88.[42]X.Liang,K.H.Chen,X.H.Chen,S.Y.Chen,G.S.Peng,Mater.Sci.Eng.PowderMetall.16(2011)290.Y.C.Lin et al./Journal of Alloys and Compounds550(2013)438–445445。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
第15卷第5期Vol.15No.5中国有色金属学报The Chinese Journal of N onferrous Metals2005年5月May 2005文章编号:10040609(2005)050763052618铝合金的热变形和加工图①黄光胜1,汪凌云1,陈 华2,黄光杰1,张所全1(1.重庆大学材料科学与工程学院,重庆400044;2.西南铝业(集团)有限责任公司,重庆401326)摘 要:在G leeble1500D热模拟仪上进行热压缩实验,研究了变形温度为573～773K、应变速率为0.01～10 s-1时2618铝合金的热变形行为。
热变形过程中的稳态流变应力可用双曲正弦本构关系式来描述,平均激活能为181kJ/mol,大于其自扩散激活能。
根据材料动态模型,计算并分析了2618铝合金的加工图。
利用加工图确定了热变形的流变失稳区,并且获得了试验参数范围内的热变形过程的最佳工艺参数,其热加工温度为623～723K,应变速率为0.01s-1,温加工温度为573K左右,应变速率为0.01s-1。
关键词:2618铝合金;流变应力;加工图;热变形中图分类号:T G301文献标识码:AH ot deform ation and processing m aps of2618aluminum alloyHUAN G Guang2sheng1,WAN G Ling2yun1,CH EN hua2,HUAN G Guang2jie1,ZHAN G Suo2quan1(1.College of Materials Science and Engineering,Chongqing University,Chongqing400044,China;2.Sout hwest Aluminium Group Co.,Ltd.,Chongqing401326,China)Abstract:The deformation behaviour of2618aluminum alloy was investigated by compression tests with G leeble 1500D thermal simulator system.The tests were performed in the temperature range between573and773K and strain rates between0.01and10s-1.The flow behaviour is described by the hyperbolic sine constitutive equation, and an activation energy of181kJ/mol greater than the activation energy for self2diff usion in Al is calculated.The processing map s were calculated and analyzed according to the dynamic materials model.The process of hot deform2 ation in the temperature range and different strain rate can be attained by the maps,which hot deformation tempera2 ture is623723K and strain rate is around0.01s-1.The warm deformation temperature is approximately573K and strain rate is also about0.01s-1.The instability zones of flow behaviour can also be recognized by the maps.K ey w ords:2618aluminum alloy;flow stress;processing map s;hot deformation 国防工业和航空工业的高速发展对耐热铝合金提出了更高的要求,2618铝合金属于Al2Mg2Cu2 Fe2Ni系锻造铝合金,是目前耐热性能最好的铝合金,被广泛应用于航空发动机及其它较高温度条件下工作的零部件[1]。
热压缩试验可获得不同条件下流变应力的连续数据,不仅可用于流变行为研究,而且还可用于计算获得材料的加工图。
加工图是变形温度与应变速率空间中的功率耗散图与失稳图的叠印。
根据加工图可以判别材料变形过程中的流变失稳区,还可根据非失稳区内最大功率耗散系数区与显微组织来制定材料的最佳加工工艺制度(变形温度与应变速率)。
关于加工图的理论在文献[25]中已有相关论述。
①收稿日期:20041112;修订日期:20050308作者简介:黄光胜(1974),男,讲师,博士.通讯作者:黄光胜,博士;电话:023*********;E2mail:gshuang@本文通过热压缩试验,获得了2618铝合金的流变应力,研究了流变应力模型及加工图,分析了材料的最佳热加工条件,为2618铝合金热加工工艺的制定与优化提供实验数据及理论依据。
1 实验实验材料为2618合金,属于Al2Cu2Mg2Fe2Ni 合金,其名义化学成分(质量分数)为:Cu1.8%～2.7%,Mg1.2%～1.8%,Fe0.9%～1.4%,Ni 0.8%～1.4%。
将经均匀化处理后的铸锭加工成d10mm×12mm的小圆柱试样,在Gleeble 1500D热模拟仪上进行圆柱体单向热压缩。
实验中在试样两端涂上高温石墨润滑剂(75%石墨+20% 46#机油+5%硝酸三甲苯脂,质量分数),为了防止碳化钨压头与试件粘连,在压头与石墨润滑剂之间放置一层厚度为0.1mm的钽片。
实验设计采用分类法,压缩温度为573～773K,间隔温度为40 K,应变速率分别为0.01、0.1、1.0、10.0s-1。
压缩前升温速度为2K/s,到温后保温5min。
相对压下量为70%。
试样变形后,立即水冷凝固变形组织。
沿压缩轴线剖开压缩试样,利用金相显微镜观察显微组织。
2 实验结果2618铝合金热变形过程中的真应力—真应变曲线如图1所示。
在一定的变形温度和应变速率下,流变应力先随应变的增加迅速升高,当真应变超过一定值后,真应力并不随应变量的继续增大而发生明显的变化,即呈现稳态流变特征。
绝大部分流变曲线为平滑直线,说明变形过程中动态回复是主要的软化机制;而有小部分流变曲线呈现出锯齿形,为典型的动态再结晶特征。
在相同的变形温度下,随着应变速率的增加,材料的真应力水平升高,该合金是一种应变速率敏感材料。
3 高温流变应力稳态流变应力的模型有多种,双曲正弦模型已广泛用于金属材料的热变形研究中[68],文献[5, 9,10]表明,对于许多铝合金的也能准确地描述其流变应力与变形温度和应变速率的关系,因此本文在研究稳态流变应力时选用双曲正弦模型,假设稳图1 不同温度时压缩的真应力—应变曲线Fig.1 Compressive t rue st ress—st raincurves at different temperat ures(a)—573K;(b)—693K态流变应力满足双曲正弦模型,即:ε・=A[sin h(ασ)]n exp(-Q/R T)(1)式中 Q为表观变形激活能;R为气体常数,8.31 J/mol;并假设A、α、n为常数,其中α可由指数关系模型(ε・=A1σn1)中的n1与幂指数模型(ε・=A2×exp(βσ))中的β共同确定,即α=β/n1=0.01245。
Zener2Hollomon(Z)参数综合了材料的热变形条件,Z参数表达式如下[11]:Z=ε・exp(Q/R T)(2)将式(2)代入式(1),得Z=A[sin h(ασ)]n(3)对式(1)两边取偏微分可得:Q=R5ln(sin h(ασ))5(1/T)ε・5ln(sin h(ασ))5ln(ε・)T(4)图2和3所示分别表示在热压缩过程中的稳态流变应力与变形温度和应变速率的关系。
・467・中国有色金属学报 2005年5月图2 ln (sin h (ασ))与温度的关系Fig.2 Relation betweenln (sin h (ασ))and temperature 图3 ln (sin h (ασ))与ln ε・的关系Fig.3 Relation between ln (sin h (ασ))and ln ε・ln (sin h (ασ))分别与T -1和ln ε・成线性关系,通过回归分析,其线性相关系数均匀在0.97以上,说明双曲正弦模型能准确描述流变应力与应变速率的关系。
通过图2和3中所示的直线的斜率可计算出合金的平均变形激活能为Q =181kJ /mol ,大于铝合金自扩散激活能。
根据图3中直线的截距,即Q/R T -ln A 的值,取其平均值可获得A =1.001×1013s -1。
而其斜率为1/n ,则可求得材料常数n 的平均值为5.09。
对式(3)两边取自然对数得:ln Z =ln A +n ln [sin h (ασ)](5)图4表明ln[sin h (ασ)]与ln Z 成线性关系,对其进行一元线性回归,相关系数为0.99。
即可用双曲正弦模型来描述2618铝合金的稳态流变行为。
图4 ln (sin h (ασ))与ln Z 的关系Fig.4 Relation between ln (sin h (ασ))and ln Z 4 加工图材料的流变应力与应变速率的关系还可表示为[3]σ=K ・ε・m(6)式中 K 为常数;m 为应变速率敏感指数。
对于2618铝合金,当温度不变时,ln σ与ln ε・的一元线性回归系数在96.3%～99.7%之间,说明ln σ与ln ε・之间存在线性关系(图5),其关系也可用式(6)来描述。
m 可由下式求得[3,4]:m =5ln σ/5ln ε・(7)图5 ln σ与ln ε・的关系Fig.5 Relation between ln σand ln ε・ 加工图是加工变量空间(应变速率,温度)中的功率耗散图与失稳图的叠印图。
功率耗散图代表材料显微组织改变时功率的耗散,其变化率可用一个・567・第15卷第5期 黄光胜,等:2618铝合金的热变形和加工图无量纲参数表示,即功率耗散系数η为[12]η=2mm+1(8)失稳图是根据不可逆热力学极值原理,用另一个无量纲参数ξ(ε・)表示大塑性流变时的连续失稳判据[5,12]ξ(ε・)=5ln[m/(m+1)]5lnε・+m(9)当ξ(ε・)<0时,为非稳态流变。