“…It is noted that a relatively longer welding cycle (5-15 s) needs to be applied to promote the IMCs layer formation when directly joining Al to uncoated steels [11,12,14], which is impractical for the mass production. Meanwhile, advanced tool material such as WC-Co [19], WC [20,22], W25Re [17,18,21], tungsten carbide [22], or silicon nitride should be used to obtain interlocking mechanism by plunging tool pin into the bottom steels [23].…”