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.
Highlights
Aluminum A357 semisolid alloys are considered to be excellent candidate materials for automotive engineering applications, especially of mechanical parts as suspension control arm
The SEED process is coupled with a high pressure die casting (HPDC) press to produce cutting standard samples of A357 semi-solid alloys of suspension control arm, used for material characterization, mainly Vickers-micro hardness, electrical conductivity measurements, tensile properties, and microstructure evolution using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) microscopy
The optimum compromise between hardness, strength, and ductility values obtained in this study aimed at enhancing the crack-failure resistance of the A357 semi solid alloys used in the fabricating of automotive parts as a suspension control arm
Summary
Aluminum A357 semisolid alloys are considered to be excellent candidate materials for automotive engineering applications, especially of mechanical parts as suspension control arm. The microstructure and mechanical properties which are attainable in these alloys are known to be strongly influenced by solidification characteristics and heat treatment parameters. The semi-solid materials, SSM, produced by Swirled Equilibrium Enthalpy Device casting technique, SEED, is an efficient technology that offers several advantages over liquid and solid processing. The semisolid casting process improves the quality of A357 aluminum alloys by inducing qualitative casting with low shrinkage problems and beneficial microstructural characteristics. This casting technique, as well as the solution heat treatment process, plays a positive role in modifying the morphology of forming spheroid.
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