Friction Stir Spot Welding of Lap Joints of Stack of Thin Sheets Made of 1565chM Aluminum Alloy

Presented are the results of investigations of the structure and properties of overlap joints of thin sheets of aluminum alloy 1565chM produced by friction stir spot welding. It was found that the highest values of destructive shear and breakoff forces of the welded spots in the alloy under investigation are observed under the following welding mode: tool rotational speed of 1000–1800 min–1 (rpm), welding time of 3 s, axial force pressing the tool of 4300–5000 N. The spot weld of a two-sheet stack of alloy 1565chM fails upon shear at a force of 2670–2720 N and upon breakoff at 1040–1100 N. After shear and breakout tests, three zones are evident in the weld spot: an indentation from the tool pin in the lower sheet, an annular zone of joint formation between the sheets of the stack, and a zone of modification of the oxide-film structure under the influence of frictional heating on the surface of the lower sheet. The destructive shear force of the spot weld of a stack of 1565chM + 1565chM sheets welded after mechanical brushing of the contacting surfaces increases from 2720 N (welding time of 3 s) to 3520–3640 N. The destructive breakoff force of the weld spot increases by approximately 25–29%.