A study on joining magnesium alloy high pressure die casting components with thread forming fasteners

With tremendous weight saving potential, magnesium alloy high pressure die casting components have been widely used for automotive applications. Magnesium fastening technology is thus becoming increasingly important to design engineers. Joining as-cast holes of magnesium high pressure die casting components with thread forming fasteners provides significant advantages for the assembly process, overall cost benefit and joint integrity. This type of joint is thus preferred for structural applications. Designing the thread forming fasteners with as-cast holes follows the general rules for designing for the machined holes, including carefully designing the variables such as the assembly torque range, the length of thread engagement, the hole diameter and required failure mode. In addition, special attention needs to be paid to the draft angles of the magnesium cast components that are required for the die casting process. In this paper, the effects of above key factors, individually and combined, on the joint performance of thread forming fasteners with as-cast blind holes of AM60B magnesium components are studied. A joint design philosophy was proposed to optimize both joint performance (the prevailing torque, the failure torque and the failure mode) and manufacturing easiness (the hole diameter and corresponding draft angle). The detailed design considerations for as-cast holes of magnesium HPDC are discussed and explained through a hypothetical example.