ENAC-46000alloy

A R C H I V E S
o f
F O U N D R Y E N
G I N E E R I N G Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences ISSN (1897-3310) Volume 10
Issue 4/2010
169 – 172
32/4
Effect of modification and heat treatment operations on impact strength of the
EN AC-46000 alloy
J. Pezda
Faculty of Chipless Forming Technology, University of Bielsko-Biała,
Willowa 2, 43-309 Bielsko - Biała, Poland
Correspondingauthor.E-mailaddress:******************.pl
Received 06.07.2010; accepted in revised form 15.07.2010
Abstract
More and more stringent requirements concerning mechanical and technological properties, which are imposed on materials used to castings of heavy duty machinery components extort implementation of modern selection methods of alloying additives (synthesis of alloys), modifying agents and heat treatment. Obtainment of optimal results, i.e. improvement of mechanical properties of processed alloy as well as its economic aspect are connected with selection of a suitable temperatures and durations of solution heat treatment and ageing operations. In the paper is present an effect of modification and heat treatment processes on KCV impact strength of the EN AC-46000 alloy. Investigated alloy underwent typical treatments of refining and modification, and next heat treatment. Temperatures’ r ange for heat treatment operations was evaluated with used of the ATD method. Obtained results concern registered curves of melting and solidification with use of the ATD method and the impact strength. On base of performed tests one has determined a range of heat treatment parameters which create conditions to suitable impact strength of the EN AC-46000 alloy.
Keywords: Modification, Heat treatment, ATD, Impact strength
1. Introduction
Nowadays, aluminum and its alloys (except iron) find the broadest implementation in any type of design structures. It is connected both with its mechanical properties and with good founding properties, good machineability and thermal conductance [1-3].
Mechanical properties of silumins are determined by their chemical composition and structure of an alloy which undergoes a changes after refining, modification and heat treatment, i.e. treatments aimed at growth of mechanical properties of the alloy. In such area are performed a comprehensive investigations, aimed at permanent growth of competitiveness of the Al-Si alloys, comparing with another structural materials [1,2,4-18].
Moreover, it is not possible to neglect an effects of technological conditions of alloy preparation, i.e. correct selection and batching of modifying agent, temperature of the metal, time elapsing from modification to solidification of the alloy, because even optimally selected modifying agent is not able to fulfill its task in case of faulty selected technological conditions.
Equally important issue is taking the best from theory of crystallization and methods based on analysis of tem peratures’ change course (ATD, DTA) as well as temperature and voltage change (ATND) [1,2,19]. These methods enable registration of crystallization processes and a phenomena occurring in course of their duration. Analysis of course of the recorded curves enables
assessment both of extend of alloy’s modification and temperatures’ range of solution heat treatment and ageing treatment [15].
Among methods of investigation of mechanical properties of alloys, the impact test constitutes a sensitive method to assess effects being result of performed processes of modification of hyper- and hypoeutectoid silumins [3].
2. Methodology of the research
The EN AC-46000 (EN AC-AlSi9Cu3(Fe)) alloy is characterized by very good casting and technological properties. Due to very good mechanical properties, this alloy is used for heavy duty components of machinery, like cylinder heads and pistons of engines.
The first stage of the investigations consisted in testing of crystallization course for the alloy. Process of solidification and melting of the alloy was recorded with use fully automated Crystaldimat analyzer.
Next, one performed treatment of refining with use of Rafal 1 preparation in quantity of 0,4% mass of metallic charge. After completion of the refining there were removed oxides and slag from metal-level and performed operation of modification with strontium, making use of AlSr10 master alloy in quantity of 0,5% mass of metallic charge (0,05% Sr).
The heat treatment was performed for the refined and modified alloy. This treatment consisted in putting the test pieces poured from the investigated alloy to solutioning and ageing. Temperatures of these treatments were selected on base of points’ values taken from curves of the ATD method.
In the Fig. 1 are shown recorded curves of heating (melting) and crystallization of refined and modified alloy, recorded with use of the ATD method, with marked temperatures of solutioning and ageing treatments.
Fig. 1. Curves of the ATD method for refined and modified
EN AC-AlSi9Cu3(Fe) alloy
In the Table 1 are shown parameters of the heat treatment for three stage plan of investigations with four variables, on base of this plan there were determined values of temperatures and durations of solutioning and ageing treatments aimed at obtainment of the best KCV impact strength of the alloy. For the assumed plan of the investigations, number of configurations amounts to 27.
Table 1.
Heat treatment parameters of the alloy
solutioning
temperature
t p [o C]
solutioning
duration
p
[h]
ageing
temperature
t s [o C]
ageing
duration
s
[h]
t p1 - 175 2 t s1 - 485 0,5
t p2 - 240 5 t s1 - 510 1,5
t p3 - 320 8 t s1 - 545 3
The next stage of the investigations consisted in the impact tests of the investigated alloy. The impact test was performed with use of the Charpy pendulum machine.
3. Description of obtained results
Impact strength of the raw alloy amounted to from 2,2 up to 2,4 J/cm2. After refining, one obtained the impact strength in range of 2,6 to 2,8 J/cm2. Modification treatment resulted in growth of the impact strength, which amounted to from 2,9 up to 3,1 J/cm2. In the Fig. 3 is presented a change of the impact strength after performed heat treatment for refined and modified alloy in all points of the plan taken to investigations.
Fig. 2. Change of the KCV impact strength of the investigated alloy for individual configurations of the testing plan
The KCV impact strength of the EN AC-46000 has reached its the highest values for the points 12, 15 and 18 (Fig. 2), where temperature of solutioning, temperature of ageing and duration of ageing were the same (t p= 510°C, t s =320°C and p=8 h), whereas
J/cm2
duration of the solutioning was different in each of these points, and respectively amounted to:
- 0,5 h for the point 12,
- 1,5 h for the point 15,
- 3 h for the point 18.
Impact strength in these points amounted to from 7,2 up to 10,9 J/cm2. The lowest impact strength of the investigated alloy was obtained for the points 20, 25, 26 (Fig. 2). Impact strength for these points was in limits of 1,5 - 2 J/cm2.
In effect of the performed heat treatment one obtained a growth of the impact strength of the alloy, reaching up to 350% with respect to not-modified alloy.
In the Figs. 3 and 4 is shown an effect of temperature and duration change of solutioning and ageing on the KCV impact strength of the investigated alloy.
Fig. 3. Effect of temperature and duration of solutioning on impact strength of the EN AC-46000 alloy
Fig. 4. Effect of temperature and duration of ageing on impact
strength of the EN AC-46000 alloy
Optimal temperature of solutioning for the investigated alloy, in aspect of change of its impact strenght, amounted to about 510°C (Fig. 3).
On change of impact strength in case of the investigated alloy has an effect duration of its ageing (Fig.4), growth of the duration causes distinct change of impact strength of the EN AC-46000 alloy.
4. Conclusions
The ATD method has enabled assessment of temperatures’ ranges of solutioning and ageing treatments of the alloy used in assumed plan of the investigations.
Proper selection of temperatures and durations of solutioning and ageing treatments enables obtainment of significant growth of impact strength of the EN AC-46000 alloy.
Selection of temperatures and durations of solutioning and ageing treatments on base of performed initial tests was completed, making evaluation of their ranges, which enable obtainment of the highest impact strength of the alloy:
a) temperature of solutioning - 500 510 o C,
b) duration of solutioning - 0,5 to 3 h,
c) temperature of ageing - 320 o C
d) duration of ageing - 8 h.
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