Investigation on wear mechanisms of PVD coatings for form taps in threading of Al–Si alloy

Form tapping of automotive engine grade Al–12Si die-cast alloy faces critical challenges with severe wear of form tap and short tool life. Typically, the lobes of the entry taper of the uncoated tap are progressively worn by both abrasion and adhesion wear. This study is focussed on the evaluation of the coating performance of 10 different PVD coatings to determine the best wear-resistant coating for this application. A novel thin multilayered in-house developed TiAlN coating performs the best in the progressive wear tests. An in-depth wear evaluation was conducted for the selected PVD coatings of the tested taps. A common wear pattern was identified for thin hard coatings on form taps for high silicon content aluminum alloy. In addition, a detailed investigation of the wear mechanisms has shown that coating fractures along the edges of the lobe in a form tap.