Friction Stir Weldability of High Tensile Strength Mg Alloy to Al Alloy

Abstract

Friction stir weldability of a fine grained high tensile strength AZ31 magnesium alloy to an Al Mg alloy A5083 was evaluated by changing joining parameters, such as tool rotating speed, welding speed and insertion position of probe. A square butt dissimilar joint without any defect was obtained at the condition of welding speed 100 mm/min, tool rotating speed 500 rpm and offset 0 mm, by using a tool with shoulder diameter of 15 mm, pin diameter of 5 mm and pin length of 3.9 mm. Higher or lower welding speeds or rotating speeds led to the lack of bonding in the joint. Defects also occurred in the case that the offset was not 0 mm, i.e. the insertion position of the probe was shifted to either Mg side or Al side, even though the tool rotating speed was about 500 rpm and welding speed 100 mm/min. The maximum tensile strength of the dissimilar joints was about 115 MPa, lower than that of Al alloy base metal (about 308 MPa). Based on transmission electron microscopy, it can be suggested that the tensile strength of the dissimilar joint is mainly controlled by the thickness of IMC layer, which consists of Al 12 Mg 17 and Al 3 Mg 2 , and mechanical interlock between magnesium and aluminum alloys. Bond strength decreases remarkably when the mechanical interlock becomes weak due to the increase of the thickness of IMC layer.

Effect of interfacial microstructure on lap shear strength of friction stir spot weld of aluminium alloy to magnesium alloy

“…Besides Al, Al 3 Mg 2 is present on the fracture surface on the AA5083 side. Several previous works 24,[28][29][30][31][32] on the mechanical properties of dissimilar welds have suggested that the weld strength is affected by the thickness of the IMC layer formed at the interface. Yamamoto et al 24 observed a marked drop of the tensile strength when the IMC layer was thicker than 1?8 mm in the butt friction stir weld of AA5083 to AZ31.…”

“…To build such vehicles, reliable processes are needed to join dissimilar materials. For a number of combinations of dissimilar metals, such as Al alloy/ steel 17,18 and Al alloy/Mg alloy, [19][20][21][22][23][24][25][26][27][28] a well known issue has been the formation of brittle intermetallic compounds (IMCs) in the welds. Since the presence of such IMCs usually reduces ductility of the welds drastically, traditional fusion welding processes, which usually produce huge IMCs in the fusion zone, are not acceptable in most cases.…”

“…Many studies [19][20][21][22][23][24][25] have attempted FSW of an Al alloy to an Mg alloy in the butt configuration. Results of such studies have shown that butt FSW of an Al alloy to an Mg alloy produce defect free welds, but that the Al 12 Mg 17 and/or Al 3 Mg 2 form at the interface between the joined alloys through solid state interfacial diffusion.…”

Investigation of latest generation pulsed fiber laser in dissimilar joining of Al and Mg alloys

“…The major issue when welding dissimilar Mg∕Al alloys is the formation of Al 3 Mg 2 and Mg 17 Al 12 intermetallic compounds (IMCs) in a large quantity, which have a detrimental effect on joint strength [4,5] . Other issues are their different physical properties (e.g., thermal expansion, conductivity) and the limited mutual solid solubility of Mg and Al [6][7][8] . Previous studies have been carried out with the goal of understanding and controlling the growth of Mg-Al IMCs [9][10][11][12][13][14] .…”

Interfacial Microstructure of CP-Ti and AZ31 Joint by Friction Stir Welding

“…Recently, the degree to which FSW can join dissimilar metals had been investigated in the combinations of Mg/Al [2][3][4][5] , Al/Ti 6) and Mg/Ti [7][8][9] . Among them, Mg/Ti dissimilar joining by FSW was investigated between Mg-Al-Zn alloy and commercial pure titanium.…”