Abstract
Rare earths are often added to copper alloys as trace alloying elements to modify the structure and improve related properties. In this study, the Cu-7.8Sn-0.16 P and Cu-7.8Sn-0.16 P-0.15La alloy strips were fabricated through full-chain process of vacuum casting, cold rolling, intermediate annealing, cold rolling and low temperature annealing process. Then, the distinctive microstructure features and mechanical properties of Cu-7.8Sn-0.16 P and Cu-7.8Sn-0.16 P-0.15La alloys were comprehensively analyzed in special view of rare earth affected phase types and property evolution. The results indicate that the addition 0.15 wt% La has effectively refined the dendrite segregation and dispersed the microporosity. Specifically, La combines with P and form a stable and dispersed micron sized LaP2 intermetallic compound, which replaces the low melting point (α+δ+Cu3P) ternary phase in the La-free alloy. Furthermore, a new nanoscale La(Cu2P)2 precipitated phase is characterized in the Cu-7.8Sn-0.16 P-0.15La alloy during low-temperature annealing process. As well, the tensile strength of Cu-7.8Sn-0.16 P-0.15La strips display notable increase to 915 MPa from 834 MPa of Cu-7.8Sn-0.16 P after low-temperature annealing. Such increase in tensile strength is attributed to the formation of La-containing phase of varied sizes in the Cu-7.8Sn-0.16 P-0.15La alloy, where the nano scale La(Cu2P)2 precipitated phase makes the most significant contribution.
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