Influence of Thermal Aging Parameters on the Characteristics of Aluminum Semi-Solid Alloys

Abstract

The current study aimed at analyzing the response of semisolid A357 aluminum alloys to unconventional thermal treatment cycles of T4/T6/T7 conditions. The mechanical, electrical, and microstructural characterizations of such semisolid alloys were investigated. The microstructure evolutions of Fe-intermetallic phases and strengthening precipitates were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The mechanical failure of such semi solid A357 aluminum alloys, used for suspension automotive parts, is mostly related to cracking issues which start from the surface due to hardness problems and propagate due to severe load variations. For these reasons, the multiple thermal aging cycles, in this study, are applied to enhance the mechanical properties and to have compromised values compared to those obtained by standard thermal treatments. The results obtained in this work indicate that the heat treatment of this alloy can be optimized. The results showed that the optimum characteristics of A357 semisolid alloys were obtained by applying thermal under-aging cycle, interrupted thermal aging cycles and a T7/T6 two steps aging treatment condition. The electrical conductivity and electron microscopy were applied in this study to analyze the characteristics of hardening phases formed due to different aging cycles applied to the alloys investigated.

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.…”

“…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].…”