Effect of Copper Oxide on Joint Strength of Friction Welding of Copper-Tungsten Sintered Alloy to Tough Pitch Copper

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The copper-tungsten sintered alloy (Cu-W) was friction welded to the tough pitch copper (TPC) and oxygen free copper (OFC), in order to investigate the effects of copper oxides included in TPC on the tensile strength of the joint. The tensile strength of the joint of Cu-W to TPC(Cu-W/TPC joint), which increased with a rise in the forge pressure P_2, was considerably lower than that of the joint of Cu-W to OFC(Cu-W/OFC joint) at P_2 below 250MPa. The low tensile strength of Cu-W/TPC joints can be attributed to uncontacted spots which could be observed on the fractured surface of the joint, since no uncontacted spot could be observed in the Cu-W/OFC joint at P_2 above 150MPa. Tensile tests at elevated temperatures and a marker experiment using alumina pouder show that the difference in the uncontacted spot can be explained by the difference in the degree of plastic flow which facilitated the attainment of intimate contact at the weld interface. On the other hand, at P_2 above 290 MPa, a fracture of Cu-W/TPC joints occurred in TPC immediately adjacent to the weld interface, in contrast to the heat affected zone of OFC in Cu-W/OFC joints, though the difference in their tensile strength became very small. On fractured surfaces of Cu-W/TPC joints, a lot of copper-oxides as well as tungsten particles picked-up from Cu-W during the friction process as reported in a previous paper were observed at dimple bottoms, suggesting that they acted as nucleation sites of fracture. In TPC adjacent to the weld interface, the copper oxide, which had a preferential distribution in the axial direction of the specimen in the base metal, was distributed preferentially in a direction parallel to the weld interface. The change in the distribution of copper oxides combined with the picked-up tungsten particles seems to cause a fracture in TPC immediately adjacent to the weld interface.
社団法人溶接学会の論文
1989-10-01

Effect of Copper Oxide on Joint Strength of Friction Welding of Copper-Tungsten Sintered Alloy to Tough Pitch Copper

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