Abstract
Manganese-bearing intermetallic compounds (IMCs) are important for ensuring adequate corrosion performance of magnesium-aluminium alloys and can be deleterious to mechanical performance if they are large and/or form clusters. Here, we explore the formation of Al-Mn IMCs in Mg-9Al-0.7Zn-0.2Mn produced by two industrial casting processes, high-pressure die casting (HPDC) and direct chill (DC) casting. As Al8Mn5 starts forming above the α-Mg liquidus temperature in this alloy, we consider its formation during melt handling as well as during casting and heat treatment. In HPDC, we focus on sludge formation in the holding pot, partial solidification of IMCs in the shot chamber, and Al-Mn IMC solidification in the die cavity. In DC casting, we focus on interactions between Al-Mn IMCs and oxide films in the launder system, Al-Mn IMC solidification in the billet, and the partial transformation of Al8Mn5 into Al11Mn4 during solution heat treatment. The results show that minimising pre-solidification in the shot sleeve of HPDC and controlling pouring and filtration in DC casting are important for ensuring small Al-Mn intermetallic particles in these casting processes.
Highlights
AZ series alloys are the most widely used Mg alloys in the automotive industry for lightweight requirements, while providing adequate strength at an acceptable cost [1,2,3,4]
The standard name of this alloy depends on the processing route: AZ91D when used for high pressure die casting (HPDC) [5], AZ91E when used for sand casting and investment casting [6,7], and AZ80A when used for forgings [8]
The aim of this study is to link from experiments on the fundamentals of Al-Mn intermetallic compounds (IMCs) formation during solidification and solution heat treatment to Al-Mn IMCs in castings produced by high-pressure die casting (HPDC) and direct chill (DC) casting
Summary
AZ series alloys are the most widely used Mg alloys in the automotive industry for lightweight requirements, while providing adequate strength at an acceptable cost [1,2,3,4]. The Al and Zn contents normally range from ~3 to 9 wt.% Al and ~0 to 2 wt.% Zn for different levels of strength and processability. For high strength AZ alloys, the mostly commonly used composition is approximately Mg-9Al-0.7Zn-0.2Mn (wt.%), with low levels of transition metal impurities. The standard name of this alloy depends on the processing route: AZ91D when used for high pressure die casting (HPDC) [5], AZ91E when used for sand casting and investment casting [6,7], and AZ80A when used for forgings [8]. AZ80A produced by direct chill (DC) casting and forging is used for wrought wheels in motor racing and high performance cars [9], as well as in structural helicopter components [10]
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