Quality Index Charts of Al-Si-Mg Semi Solid Alloys Subjected to Multiple Temperatures Aging Treatments and Different Quenching Media

Abstract

The use of quality index charts is considered as an effective mean for evaluating the mechanical performance of Aluminum alloys for industrial engineering applications. The current study was carried out to investigate the influences of multiple-interrupted temperatures aging and quenching media (water versus air) on the quality index performance and precipitations evolution of A357 Aluminum semi solid alloys. Regarding the lack of similar investigations applied on such alloys, the quality index charts were generated for Al-Si-Mg semi solid castings based on its tensile properties. These charts are used to determine the quality index, in MPa, as a simple mean for compromising the strength and ductility together in one value using the Drouzy model. The multiple temperatures aging cycles were applied to improve the quality index values of Al-Si-Mg semi solid alloys for enhancing its characteristic and performance to resist the mechanical failures relating to automotive dynamic parts. The evolution of Mg2Si hardening precipitates, formed for specific thermal aging cycles, was investigated using transmission electron microscopy (TEM). The results obtained in this work revealed that the optimum quality index values were obtained by the application of T6-thermal under-aging treatment cycles. The regression models, using a statistical design of experiments, indicated that the optimum strength and high-quality index values were obtained by the application of interrupted thermal aging cycles, mainly C2,3-T6/T4/T7 conditions.

Fatigue Cycles and Performance Evaluation of Accelerating Aging Heat Treated Aluminum Semi Solid Materials Designed for Automotive Dynamic Components

“…The standard samples and the applicable parts were prepared by the rheocasting semi-solid process using A357 aluminum alloy billets (Al-7%Si-0.65%Mg-0.1%Fe) as applied in [14,15]. The semi solid casting process is coupled with a high pressure die casting (HPDC) press to produce the materials used for mechanical and micro-structural characterizations.…”

“…These thermal aging treatments were applied to the bending fatigue standard samples and to the applicable suspension mechanical components. Specific aging cycles, mainly T6, WA0, WA1, WB0, WC1, and WC3, were applied in this study according to their positive effects on both tensile and quality index characteristics by previous studies applied for A357 aluminum semi solid alloys [14,15]. The bending fatigue samples were subjected to two step solution heat treatments, followed by water quenching maintained at 60 • C and then naturally aged at room temperature for 24 h before proceeding to the thermal aging cycles.…”

“…It is well known that the fatigue performance is highly affected by the strength and ductility properties of the aluminum matrix. A good combination of excellent strength and high ductility can postpone the fatigue cracking failure and increase the fatigue life-number of cycles [14][15][16][17]. For these reasons, the accelerating multiple thermal aging cycles of WC3 were applied to enhance the fatigue mechanical properties, by having compromised values of optimum strength and acceptable ductility compared to those obtained by standard thermal treatments.…”

“…The explanation of the high strength and ductility was related to the presence of different precipitate sizes of Mg 2 Si. Other studies [14,15] applied TEM study on the effect of multiple thermal aging treatments on performance and precipitate evolution of A357 semi-solid samples. Moreover, the formation of different sizes of Mg 2 Si precipitates that compromise between excellent strength and high ductility was observed.…”

“…The strengthen precipitates showed large differences in sizes as a result of the multiple thermal aging cycles [14]. Therefore, applying the multiple step thermal aging cycles to the aluminum semi-solid casting alloy in the manufacturing of the suspension control arm is expected to increase the total fatigue life of this component [15][16][17].…”