Tool wear of four different grades of high speed steel (SKH4, SKH51, SKH55, SKH57) in machining 7075 aluminum alloy given T6 treatment were examined. In order to know the wearing process, the worn rake faces were probed by EPMA after measuring the flank wear. SKH57 tool provides the best performance in the four tools. In the case of SKH4, SKH51 and SKH55 tool, the wear of the cutting edges and plateau part progress by delamination of deposits due to diffusion and adhesion between the work and tool materials at this area, while the crater wear is caused by abrasive action of chip flow containing hard metallic compounds. The wear of SKH57 tool due to diffusion and adhesion at plateau part is the smallest, therefore, the edge remains clearly. It is found that larger carbide grains containing tungsten in high speed steel resist the progress of abrasive wear induced by chip flow.
