Cyclic Deformation Behavior of Friction Drilled Internal Threads in AlSi10Mg and AZ31 Profiles

Abstract

Metallic lightweight materials are used for enhancing dynamic range, resource optimization and emission reduction in many fields of traffic engineering, whereby aluminium and magnesium components are manufactured by means of welded, adhesive and screw joints. Friction drilling, as forming process with subsequent manufacturing of threads, offers the opportunity to produce an internal thread in lightweight profiles with a usable thread depth larger than the profile thickness, making use of local material expansion. Moreover, the direct manufacturing offers a huge potential for time and cost saving in comparison to conventional thread machining.Microscopic-based characterization of mechanical properties of aluminium AlSi10Mg and magnesium AZ31 internal threads in thin-walled profile specimens was carried out using tensile tests and fatigue tests in tensile loading range. The internal threads were chipless manufactured by means of thread forming. Variations in the geometric process parameter wall thickness were compared. Differences between the AlSi10Mg chill casting alloy and the AZ31 continuous casting alloy in maximum tolerable loads and fatigue limits were correlated with the production-related profile qualities of the profile specimens. The maximum tolerable loads increase linearly with increasing wall thickness of the specimens, whereby AlSi10Mg specimens were about 20-24% lower in the quasi-static range and about 37-47% lower in the cyclic range in comparison to AZ31 specimens due to oval forms of the core holes caused by the friction drilling process. Plastic strain behavior and deformation-induced changes in temperature in load increase tests were evaluated to reliably estimate the fatigue limit of magnesium AZ31 internal threads.