Modificated microstructure and enhanced mechanical properties of Cu-Sn-P alloy with rare earth La addition

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-0.16P and Cu-7.8Sn-0.16P-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-0.16P and Cu-7.8Sn-0.16P-0.15La alloys were comprehensively analyzed in special view of rare earth affected phase types and property evolution. The results indicate that the addition 0.15wt.% 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-0.16P-0.15La alloy during low-temperature annealing process. As well, the tensile strength of Cu-7.8Sn-0.16P-0.15La strips display notable increase to 915MPa from 834MPa of Cu-7.8Sn-0.16P 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-0.16P-0.15La alloy, where the nano scale La(Cu2P)2 precipitated phase makes the most significant contribution.