Experimental investigation and thermodynamic prediction of new class of thixoformable magnesium alloys

Abstract

There is a thirst for light materials in the automotive and aerospace industries, which has been a strong driving force behind magnesium alloy research over the past two decades. Among the various alloys, AZ91 is the most widely used because of its good combination of castability and low cost. However, the creep resistance (gt 120 and#730;C) of these alloys are poor due to low thermal stability of Mg17Al12 phase, which restricts the usage of Mg alloys for power train applications. In order to widen the usage of magnesium alloys in the automotive sectors, there is a demand for new creep resistant Mg alloys. Generally, many of the commercial magnesium alloys are made using High Pressure Die-Casting (HPDC), which can directly fabricate the component in the liquid state. However, porosity occurs in die-castings from the turbulent flow of the molten metal into the die cavity. In addition, magnesium possesses poor formability, difficult to be deformed at room temperature because of its hexagonal closed packed structure. To overcome these problems, Semi-Solid Metal (SSM) processing has been extensively studied. SSM processing is an advanced method for material forming using the thixotropic behavior of materials with non-dendritic microstructure in the semisolid state to form near net shaped products. The main purpose of the present study is to identify a suitable creep resistant Magnesium alloy amenable for thixoforming processing. The criteria we have selected for the evaluation of thixoformability are as follows: Solidification interval, fraction liquid sensitivity, highest knee point and processing window. However, the perfectly suited and commercially used alloys for SSM processing are very limited in types. newline