2017 Volume 58 Issue 1 Pages 39-45
Vacuum die castings of AZ91D magnesium alloy were produced at different slow shot speeds and the correlation between density and microstructural features in the vacuum die castings were investigated. The density was measured by using Archimedes method. The microstructure was analyzed with optical microscope, scanning electron microscopy and image analysis software. It was found that the partially solidified gate can be early closed-off by large-size particles at low enough slow shot speeds, which causes high levels of porosity in the vacuum die castings and thus low densities of the castings. Archimedes method is not suitable for evaluating the porosity level in the vacuum die castings. Besides the porosity levels, the densities of the vacuum die castings are related to the ESCs contents in the castings and solidification conditions in the shot sleeve at the beginning of die filling.