Optimization of Heat Treatment Parameters of AlSi7Mg Alloy.

Jacek Pezda

doi:10.3390/ma15031163

Abstract

Constantly growing requirements concerning the quality of poured machinery components give rise to the need to find new solutions to improve their mechanical and technological properties, considering economic and ecological aspects resulting from energy consumption of the casting and heat treatment processes. This study presents the investigation of the effect of heat treatment on mechanical properties (tensile strength Rm, elongation A5, hardness HBW) of the AlSi7Mg alloy without modification and modified with strontium. Obtained results allowed us to determine T6 heat treatment parameters associated with the improvement of mechanical properties of the alloy with simultaneous limitation of duration of solutioning and aging treatments. The maximum increase in Rm was 67%, and 55% in the case of HBW, with a slight decrease in elongation (approx. 10%) in relation to an alloy not subjected to heat treatment in the adopted scope of tests for the total time of heat treatment of 4–6 h. The increase in elongation of up to 250% requires aging at a temperature exceeding 300 °C, which also causes a decrease in durability and hardness by 20%. Modification of the alloy using strontium before heat treatment facilitates the process of fragmentation and balling of silicone precipitates.

Highlights

The alloys belonging to the Al-Si group, due to their parameters, are widely used in the aviation and automotive industries
Performing modification of the AlSi7Mg alloy prior to its heat treatment does not have any significant effect on the obtained tensile strength and hardness; this facilitates fragmentation of silicon precipitates and their spheroidization during T6 treatment, which in turn leads to significant improvement in ductility and impact strength of the alloy
The spatial diagrams illustrate the effect of the heat treatment parameters on selected mechanical properties obtained on the base of the assumed area of the testing

Summary

Introduction

The alloys belonging to the Al-Si group, due to their parameters, are widely used in the aviation and automotive industries. Very often, they require improvement of their mechanical properties due to high operational requirements for heavily loaded components that must feature a high degree of reliability. An effective method of hardening materials, enabling considerable improvement of their mechanical properties, uses the phenomena of decreasing solubility of alloying elements in the solid-state as the limit temperature decreases [1,2,3,4]. During the first one (solutioning), the alloy is heated at a temperature above the limit of solubility in the area of a single-phase solid solution and is rapidly cooled down. In the case of alloys containing Cu or Mg, the hardening occurs due to the precipitation of Al2Cu Mg2Si and Al2CuMg phases [1,5,6,7,8]

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Conclusion