Friction Welding of Copper-50 Mass% Tungsten Sintered Alloy to Oxygen Free Copper
Masatoshi Aritoshi, Kozo Okita, Toshio Enjo, Kenji Ikeuchi
In order to investigate effects of tungsten (W) content on the friction welding of copper-tungsten sintered alloy (Cu-W alloy) to oxygen free copper (OFC), the tensile strength of joints between Cu-50%, W alloy and OFC obtained under various welding conditions has been compared with that of the joint between Cu-70%W alloy and OFC which was reported in a previous paper. The strength of Cu-50%W/OFC joint and Cu-70%W/OFC joint was increased with rise in forge pressure P2, and saturated at P2 above 250 MPa. At P2 above 150 MPa, however, the tensile strength of the Cu-50%W/OFC joint was considerably lower than that of the Cu-70%W/OFC, though both the axial displacement and friction torque during the welding for the former were much larger than those of the latter. On the tensile test, fracture of the Cu-50%W/OFC joint welded at P2 above 150 MPa was initiated in the Cu-W alloy adjacent to the weld interface and propagated along the weld interface, while the Cu-70%oW/OFCC joint was fractured in the heat affected zone of the OFC. in the Cu-50%W/OFC Joint, the W content of the Cu-W alloy adjacent to the weld interface was increased significantly compared with that of the base metal, and cracks were formed in the region where the W content was increased. It is considered that these cracks were responsible for the initiation of fracture in the Cu-50%W alloy next to the weld interface and for the lower strength of the Cu-50%W/OFC joint than that of the Cu-70%W/OFC joint. The increase in the W content and the formation of the crack became more remarkable with the increase in axial displacement during the welding, suggesting that these were caused by the plastic deformation of the Cu-50% \V alloy durnig the welding. The formation of the crack was avoided by decreasing the amount of the plastic deformation of Cu-50%W alloy, i.e., by increasing the friction speed and decreasing friction and forge pressure.