The microstructure and bond strength of the friction-welded joint of Al (commercially pure aluminum) to Cu-W (copper-tungsten sintered) alloy of various W contents have been investigated with particular reference to effects of W particles on the formation of intermetallic compounds at the weld interface and on resulting mechanical properties of the joint. A lot of mixing layer of Cu, Al and W was formed by picking-up of Cu and W into Al in the joint of Al to Cu W alloy of W content less than 30 mass%, whereas no mixing layer was found for W contents more than 50 mass%. Since the mixing layer included a number of brittle intermetallic compound layers, tensile strength for joints of Al to Cu-W of W contents below 30 mass% was considerably lower than those of W contents above 50 mass%. The highest temperature of friction interface during the friction-welding, estimated from thermoelectric power between Cu and Al, was about 800 K both for the joint of Al to Cu-W including 70 mass% W and for the joint of Al to oxygen free copper (including no W particle). Microhardness of the Cu-W alloy with 50 mass% W was significantly higher than those of W contents below 30 mass% at temperatures ranging from room temperature to 800 K. This suggests that the flow stress of Cu-W alloys containing W above 50 mass% was significantly higher than that of W contents below 30 mass%. This difference in the flow stress of the Cu-W alloy prevented the formation of the mixing layer in the joint of Al to Cu-W alloy of W contents above 50 mass%, since it needed plastic flow and rupture of Cu-W alloy to pick up Cu and W from Cu-W alloy into Al.
