Macro images of the samples welded by (a) the cylindrical tool in two passes from the Al side with rotational and traversing speeds of 800 rpm and 12 mm.min⁻¹ (sample number 4), (b) the thread tool in two passes from the Al side with rotational and traversing speeds of 800 rpm and 12 mm.min⁻¹ (sample number 5), (c) the conical tool in one pass from the Cu side with rotational and traversing speeds of 800 rpm and 12 mm.min⁻¹ (sample number 7), (d) the conical tool in one pass from the Cu side with rotational and traversing speeds of 1250 rpm and 6 mm.min⁻¹ (sample number 11).