Effect of homogenization annealing on microstructure and properties of Cu-Ni-P alloy
The homogenizing annealing treatment of as-cast Cu-Ni-P alloy was carried out at different temperatures(850,900 and 950 ℃)for different time(1,2 and 3 h)to determine a optimal annealing temperature.Different time homogenization annealing treatments were carried out at the optimal temperature to determine the optimal holding time and obtain the optimal homogenization annealing process for the alloy.Microstructure and properties of the Cu-Ni-P alloy in as cast state and after homogenization annealing were compared and analyzed.The results show that the as cast Cu-Ni-P alloy exhibits severe segregation,dendrites are haphazardly distributed,the length of the primary dendrite arm is significantly longer than that of the secondary dendrite arm,and there are a large number of second phase particles in the dendrite gap.The conductivity of the as cast alloy is 49.5％IACS,the hardness is 85.6 HV,and the tensile strength is 204 MPa.Homogenization annealing can significantly eliminate dendrite segregation in the Cu-Ni-P alloy,and the improvement effect of temperature on dendrite segregation is greater than that of holding time.The optimal homogenization annealing process for the alloy is 900 ℃×4h.The conductivity,hardness and tensile strength of the alloy treated by the optimal process are 38.9％IACS,113.8 HV and 290 MPa,respectively.Compared with the as cast alloy,the conductivity decreases,but the tensile strength and hardness increase by 42.2％and 32.9％,respectively.The tensile fracture analysis shows that the alloy belongs to ductile fracture before and after homogenization annealing treatment.
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