Abstract
Magnesium alloys have generated renewed interest as a light alloys; replacing some conventional structural materials for weight reduction in applications like aerospace, automotive and electronics industries. In interior components and powertrains, cast alloys are widely used and represent more than 99% of magnesium alloys used today, whereas only a few wrought products are used. Mostly in automotive applications, Mg-engine block can noticeably reduce the weight and consequently its fuel consumption and environmental impact. Due to solid-state precipitates, these alloys are strong in nature and are produced by an age-hardening heat treatment process. In the present work the age hardening behavior of the as cast Mg–Zn–Al alloys (ZA85 alloy) in the composition of 8 wt. %Zn, 5 wt. %Al has been investigated. Through the differential thermal analysis (DTA) studies, it has been found out that dissolution temperature of ternary eutectic precipitates is present in the alloy. Based on the DTA results, the as cast samples have been solutionised at 360 °C temperature for different intervals of time. Solutionising time has been optimized from the enthalpy values of un-dissolved precipitates. The solution treated samples have been then aged at temperature of 180° C for different time intervals. From the peak hardness values, the ageing conditions have been optimized.
Highlights
Magnesium alloys is a promising material for the fabrication of automotive, aerospace and electronics components
In order to improve the hardness of magnesium alloys, solid solution, grain size and dislocation density strengthening which either depends on the composition and thermal treatment processes had been widely studied, but precipitation strengthening mechanism has the highest strengthening effect
The Mg-Zn alloys with addition of Ca has been reported to increase the effectiveness of precipitation hardening when the alloy is exposed to ageing, causing a higher quantity of finer and uniformly dispersed precipitates, that influences the final texture of the alloy significantly [2,3,4,5] and Ca addition decreases the grain size in microstructure that leads to improvement in mechanical properties of the alloy [6], it decreases the flammability of the alloy and increases creep and oxidation resistance [7,8,9,10,11]
Summary
Magnesium alloys is a promising material for the fabrication of automotive, aerospace and electronics components. The precipitation hardening involves the addition of alloying elements along with heat treatments in order to synergistically bring about the strengthening required for the Mg alloy. These had been the focus of numerous investigations in recent times. It is reported that ZA85 alloy is one such alloy system having superior elevated temperature behaviour and satisfies the requirement of other corrosion and foundry properties [19] The mechanical properties such as strength, ductility and fracture toughness of this alloy can be further improved by adopting suitable heat treatment procedure. The present work investigated the age-hardening behaviour of the as cast Mg–Zn– Al alloys (ZA85 alloy) using DTA studies and other conventional methods
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