Thread-forming fasteners for tapping and fastening into magnesium alloys

摘要

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.