Jonathan P. Weiler

Intermetallic formation in sludge during magnesium (Mg) melting, holding and high pressure die casting practices is a very important issue. But, very often it is overlooked by academia, original equipment manufacturers (OEM), metal ingot producers and even die casters. The aim of this study was to minimize the intermetallic formation in Mg sludge via the optimization of the chemistry and process parameters. The Al₈Mn₅ intermetallic particles were identified by the microstructure analysis based on the Al and Mn ratio. The design of experiment (DOE) technique, Taguchi method, was employed to minimize the intermetallic formation in the sludge of Mg alloys with various chemical compositions of Al, Mn, Fe, and different process parameters, holding temperature and holding time. The sludge yield (SY) and intermetallic size (IS) was selected as two responses. The optimum combination of the levels in terms of minimizing the intermetallic formation were 9 wt.% Al, 0.15 wt.%Mn, 0.001 wt.% (10 ppm) Fe, 690 °C for the holding temperature and holding at 30 mins for the holding time, respectively. The best combination for smallest intermetallic size were 9 wt.% Al, 0.15 wt.%Mn, 0.001 wt.% (10 ppm) Fe, 630 °C for the holding temperature and holding at 60 mins for the holding time, respectively. Three groups of sludge factors, Chemical Sludge (CSF), Physical Sludge (PSF) and Comprehensive Sludge Factors (and CPSF) were established for prediction of sludge yields and intermetallic sizes in Al-containing Mg alloys. The CPSF with five independent variables including both chemical elements and process parameters gave high accuracy in prediction, as the prediction of the PSF with only the two processing parameters of the melt holding temperature and time showed a relatively large deviation from the experimental data. The Chemical Sludge Factor was primarily designed for small ingot producers and die casters with a limited melting and holding capacity, of which process parameters could be fixed easily. The Physical Sludge Factor could be used for mass production with a single type of Mg alloy, in which the chemistry fluctuation might be negligible. In large Mg casting suppliers with multiple melting and holding furnaces and a number of Mg alloys in production, the Comprehensive Sludge Factor should be implemented to diminish the sludge formation.

High-pressure die-cast (HPDC) magnesium alloys have seen diverse applications in the automotive industry, primarily driven by requirements in internal combustion engine (ICE) vehicles. As the automotive industry is transitioning to an electric vehicle (EV) architecture, there is a great potential for novel applications to improve driving range efficiency. In addition, there is a trend toward larger-sized automotive die castings and an increased interest in aerospace applications due to weight reduction. In this chapter, we reviewed the traditional automotive structural applications in ICE vehicles, as well as current and potential future EV and aerospace applications of HPDC magnesium alloys. The structural applications using AM50, AM60, AZ91 and AE44 magnesium alloys in traditional vehicles can be applied to modern EVs. Additionally, magnesium alloys with varying degrees of higher thermal conductivity, improved castability, superior high temperature properties and flammability need to be developed to replace battery and aerospace in-cabin-related structural materials to meet all safety requirements. Several newly developed magnesium alloys with superior castability are also reviewed for potential automotive and aerospace applications.