Step-by-Step Observation of Secondary-Phase Evolution During the Casting Cracking Process in Mg-Ce-Al Alloys

Secondary phases are key factors affecting cracking behavior during casting, but it is still unclear how exactly cracks form. The cracking susceptibility of die-cast Mg-Ce-Al series alloys, which are used in heat-dissipating components in the communication industry, varies greatly with the evolution of the secondary phase. In this paper, a high-temperature tensile test was employed to simulate the tensile behavior during the casting cracking process according to the load-temperature-cooling rate-time curves, to study the effects of secondary-phase evolution on crack nucleation and propagation step by step. Based on the Mg-Ce-Al alloy system, three alloys with the same secondary-phase fraction (similar to 7 pct) were designed using the Pandat software: Mg-3.0Ce (Mg12Ce), Mg-7.5Al (Mg17Al12), and Mg-9Ce-6.5Al (Al11Ce3 + Al2Ce). The high-temperature tensile test results showed that Mg12Ce was relatively brittle and cracks easily nucleated with it; Mg17Al12 easily dissolved and then promoted crack nucleation and propagation. In addition, cracks also propagated along the weak Mg12Ce/Mg and Mg17Al12/Mg interfaces. The bulk Al2Ce particles easily cracked or detached from the alpha-Mg matrix to induce crack nucleation. Fortunately, the fine and dispersed Al11Ce3 significantly improved the high-temperature mechanical properties to help resist cracking and did not induce crack nucleation or propagation. (c) The Minerals, Metals & Materials Society and ASM International 2022