Effect of grain refiner and grain size on the susceptibility of Al–Mg die casting alloy to cracking during solidification

The die casting process and its alloys have been developed in recent years for automobile body parts such as B-pillars. However, it is known that die casting alloys with high ductility and fracture elongation often show a higher susceptibility to cracking during solidification than conventional Al–Si alloys. Thus, it is important to estimate and control the susceptibility to cracking during solidification before trial casting or mass-production. In this study, as a representative non-heat treatment type alloy, Al–4.5wt%Mg (JIS AC7A, AA 514) aluminum alloy was used. The effect of the addition of silicon and grain refiner on the reduction of the susceptibility to cracking was examined. In order to evaluate the susceptibility to cracking, both the “I-beam casting cracking test” and the “TIG spot welding cracking test” were carried out. As a result, the addition of Ti + B worked as a grain refiner on both testing methods. The susceptibility to cracking was significantly reduced by the addition of Ti + B in both the I-beam casting and the weld crater. It was found that the finer grain size led to lower susceptibility to cracking. Furthermore, the susceptibility to cracking of the die casting product decreased with the addition of Ti + B.