1st ICAI 2020

International Conference on Automotive Industry 2020

Mladá Boleslav, Czech Republic

Figure 2: Hexagonal Close-packed lattice (whole atoms and unit cell)

Source: own elaboration 2.1 Properties of magnesium alloys

Very rarely is magnesium used in industrial applications as pure magnesium. In the vast majority of case is alloyed with other metals. The basic influence of the most important alloying element can be summarized as following: Al – improves castability and precipitation hardening at low temperatures; Cu – improves castability and creep properties; Mn – refinement of precipitates and improves creep resistance; Si – decreases castability, forms stable silicide compounds and improves creep properties; Th – suppresses microporosity and improves ductility; Zn – increases fluidity of the melt and improves strength at ambient temperatures; Zr – most effective grain refiner (Polmear, 2006). Generally, it can be stated that great advantages of using magnesium alloys (very low density, possibility to cast thin castings) are strongly negated by their limited availability as sheets and especially by their high costs. Moreover, the use of magnesium for components operating at higher temperatures remains problematic. The decrease in the mechanical properties of magnesium alloys can be observed already above 150°C (Serak, 2014) 2.1.1 Cast magnesium alloys – basic overview Historically, cast magnesium alloys represent a vast majority (c. 85 %) of all products. Nowadays are cast magnesium alloys, where nominal composition and typical tensile properties of the most important alloys is shown in Table 1, mostly produced by high- pressure die casting (both cold and hot-chamber). The greatest problem of such pressing technology rests in relatively high levels of porosity (Polmear, 2006). Sand casting and low-pressure die casting is used for castings having not very complicated shape. Moreover, when it is necessary to produce high-quality castings from magnesium alloys, squeeze casting and thixo-moulding (reduction of microporosity) are these days used as well.

48