Novel dissimilar spot welding of aluminium alloy and steel sheets by friction stirring

Interfacial bonding mechanism in Al/coated steel dissimilar refill friction stir spot welds

“…Conventional friction stir spot welding (FSSW) is a relatively new solid-state joining technology, which is a natural alternative to fusion welding due to that it avoids the problems of solidification and liquation cracking [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Mazda has used conventional FSSW to join Al alloy to coated steels in aluminum trunk lid [27], acceptable weld strength was achieved although keyhole significantly decreased effective bonded area [11][12][13][14][15].…”

“…Mazda has used conventional FSSW to join Al alloy to coated steels in aluminum trunk lid [27], acceptable weld strength was achieved although keyhole significantly decreased effective bonded area [11][12][13][14][15]. There are three main approaches of joining Al alloy to steel by conventional FSSW: (i) directly joining Al to uncoated steel through the formation of IMCs while avoiding plunging the tool pin into bottom steels [11][12][13][14][15][16], (ii) mechanical interlocking by displacing the bottom steel into the Al sheet [17][18][19][20][21][22][23], and (iii) adoption of coatings on steels to promote the interfacial bonding [24][25][26][27][28]. 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.…”

“…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].…”