Influence of elevated temperature on mechanical properties of friction drilled internal threads in AlSi10Mg, AZ31 and AZ91 profiles

Wittke, P.1, a; Teschke, M.1; Hannich, S.2, b; Biermann, D.2, c; Walther, F.1, d

Fachgebiet Werkstoffprüftechnik (WPT), TU Dortmund
Institut für Spanende Fertigung, Technische Universität Dortmund, Baroper Str. 303, 44227 Dortmund

a); b); c); d)


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. Microstructural-based characterization of mechanical properties of aluminium AlSi10Mg and magnesium AZ31 and AZ91 internal threads in thin-walled profile specimens was carried out using tensile tests and fatigue tests in tensile loading range with load ratio 0.1 at room temperature and 110 °C. The internal threads were chipless manufactured by means of thread forming. Variations in the geometric process parameters wall thickness and thread depth were compared. Differences between the AlSi10Mg and AZ91 chill casting alloys and the AZ31 continuous casting alloy in maximum tolerable loads and fatigue limits were correlated with the production-related profile qualities and changes in microstructure of the profile specimens. The maximum tolerable loads at room temperature 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. Micro-hardness mappings show work hardening at the edge area of AZ31 thread flanks with an increase of about 108% in contrast to the basic hardness. Plastic strain behaviour by means of mechanical stress-strain-hysteresis- and DIC-measurements and deformation-induced changes in temperature in load increase tests were evaluated to reliably estimate the fatigue limit of aluminium and magnesium internal threads at room and elevated temperature. The results were validated in constant amplitude tests until 1E7 cycles.


LightMAT 2017, Proceedings of the 2nd International Conference on Light Materials, 08.-10.11.2017, Bremen, (2017)