Cu-9ni 2.5sn-1.5al-0.5si Alloy Heat Treatment Process And Performance Research

In this paper, by the means of metallomicroscopy, SEM, TEM, energy spectrum and the measurement of conductivity and hardness, the effect of added 0.5%Si and 1.5%A1 on the microstructure and properties of Cu-9Ni-2.5Sn alloy is studied. It is found that:(1) The cast structure of Cu-9Ni-2.5Sn-0.5Si-l.5%A1 alloy has three zones:Treelike crystal is inner layer consisted of Cu-Ni solid solution with poor Sn and rich Ni. Outer layer of treelike crystal is rich Sn phase , Ni2Si and Ni2Al phases containing a little Cu. These phases are consisted of the second layer. Between two layers, it is complex structural transitional zone.(2) There exists Sn negative segregation in the cast structure by macro-observation and the content of Sn decreases from outside to inside. The action of homogenized annealing can eliminate the segregation of treelike crystal, however, not eliminate Sn negative segregation.(3) Temperature increasing of homogenized annealing can greatly reduce time of homogenized annealing. Too high temperature makes alloy overburning, produce burnt structure in grain boundary. Proper homogenized annealing technology is 960 ℃\ 1 hours.(4) Added little Si and Al in Cu-9Ni-2.5Sn alloy produce Ni2Si and Ni2Al phrase. During ageing, Ni2Si and Ni2Al precipitation makes conductivity increase.(5) During ageing, the ageing hardened curve is the shape of unimodal. With the increasing of ageing temperature, time is shortened reaching hardness peak. It takes 1.5 hours at 480癈 ageing, 3.5 hours at 450癈 ageing. The peak of them is not different greatly. Ni2Si phase produces additional deposited harding so that the hardness of Cu-9Ni-2. 5Sn-l. 5A1-0. 5Si alloy is higher than Cu-9Ni-2. 5Sn alloy.(6) For Cu-9Ni-2. 5Sn-l. 5A1-0. 5Si alloy , that the cold is greater before ageing is favorable for its precipitation-hardening during ageing and the time arrived toABSTRACTpeak strength is shortened(7) In the sample of peak strength during ageing, we obtain two kinds of diffraction spots of matrix and precipitate. These diffraction spots are indexed .On the basis of it , we know that the orientation relation between the matrix and precipitate has been found to be:(H0)m//(21l)m- [110]m//[324]pp,(8) The material is strengthened by the precipitate in Cu~9Ni-2. 5Sn-l. 5A1-0. 5Si alloy by Orowan mechanism, namely, the dislocation passes round the precipitate and leaves a dislocation loop. When the second-phase in the ageing-hardening alloy generates strengthening effect by Orowan mechanism, the increasing strengthen is inverse proportion to the average spacing of the precipitate among the matrix. The capacity fraction of the precipitate in material is fixed. The smaller the precipitate's size is, the larger its amount is and the smaller the average spacing is, so that the strengthening effect is more significant.