Automotive Magnesium Die Casting Through Thermal and Flow Control

Some causes for hot cracking in automotive magnesium casting were studied through thermal and fluid flow analysis. Solidification of magnesium alloy casting is found to start early, but complete late. There are small amount of residual liquid phase staying at the eutectic temperature. This property is the main reason that magnesium castings crack. The different solidification defect patterns between the center and skin of castings are analyzed. Some crack prevention techniques and criteria are introduced to obtain better solidification pattern, which leads to higher quality castings.

Separation and filling reversal are also frequently causing magnesium castings to crack. Through the study of the flow atomization number and the Reynolds number, the magnesium casting filling process is found to be a typical turbulent flow process. The optimized flow pattern with necessary design changes is introduced to generate better flow results during mold filling.

Several real automotive magnesium die casting parts are used as examples, coupled with some thermal and fluid flow concepts, tables and process simulations results to illustrate the positive and negative experiences in the automotive magnesium die casting manufacturing.