Thread Forming Fasteners for Tapping and Fastening into Magnesium Alloys 1999-01-0923

The applications for components and complete assemblies using magnesium are ever increasing. There are a number of methods of joining or attaching magnesium components and the use of threaded fasteners are quite often the preferred choice. A new type of thread forming fastener has been designed specifically for magnesium to overcome the limitations of other conventional threaded fasteners. This paper will describe this new fastener and compare its thread forming performance to conventional thread forming fasteners. The topics to be covered are: 1. Comparative multiple removal and reinsertion; 2. Drive torque (thread forming torque), failure torque, clamp load and nut factor as a function of percent thread engagement into AZ91, AM50 and AZ31; 3. Validation of percent thread engagement; 4. Distance to no measurable edge distortion; 5. Retained clamp load at room temperature and 125°C for the new thread former and machine screw in AZ91, AM50 and AZ31; 6. Repair procedure; 7. Confirmation of tensile stress area; 8. Tensile pull out load capability; 9. Galvanic corrosion; 10. First removal torque; and 11. Die cast cored hole versus drilled pilot hole.