Charracterization Of Precipitates In Cu-rich Solid Solution Corner Of Cu-Ni-Al Temary Phase Diagram And Heat Treatment Crafts

With the rapid development of modern industry and science technology,not only the material needs to have high conductivity,but also has high strength and good wear resistance.Cu-Ni-Al alloy satisfies the composition selection of high-strength alloy.At present,the copper-rich end on the 500?isothermal cross-section of Cu-Ni-Al ternary phase diagram is considered to be ?-(Cu,Ni)single-phase solid solution zone.The solid solution is the most severe damage to the conductivity of the copper matrix,consequently,from the phase diagram,Cu-Ni-Al alloy does not have high strength potential.In fact,the copper-rich end of the Cu-Ni-Si ternary alloy is also viewed as a single-phase solid solution zone,however experiments have shown that when the Ni and Si contents are very low,the Cu-Ni-Si alloy can generate the precipitated phase.By analogy,the copper-rich single-phase region of Cu-Ni-Al ternary phase diagram is probable to generate the precipitated phase.As aresult,the fact that there is a precipitation phase at 500? isothermal section copper-rich end single-phase region of Cu-Ni-Al ternary phase diagram is proved,which is the key for the use of Cu-Ni-Al alloy as high strength materials.In this paper,the smelting method was used to prepare Cu-Ni-Al alloy that meets the composition requirements,and the feasibility of the precipitation phase was proved.The solution and aging treatments of the alloy were performed by orthogonal experiments to study the impacts of heat treatment process on the properties of the alloy and to determine the best heat treatment process.The main conclusions of this article are as follows:(1)The as-cast Cu-5.4Ni-3.6Al and Cu-4.2Ni-2.8Al alloys prepared by smelting method have the rod-shaped precipitation phases in the grain.Through characterization,the precipitation phase is determined to be NiAl phase.Then the as-cast Cu-5.4Ni-3.6Al and Cu-4.2Ni-2.8Al alloys were heat treated by solution treatment and aging process of 800?×4h+500?×4h.Cu-5.4Ni-3.6Al and Cu-4.2Ni-2.8Al alloy have nano-sized granular precipitates in the crystal.Through characterization,the granular precipitates are determined to be Ni3Al phases.Therefore,the feasibility of the precipitation of precipitated phases in the single-phase solid solution zone of the Cu-Ni-Al alloy ternary phase diagram at 500? with isothermal section at the copper-rich end is proved,which provide theoretical and experimental basis for Cu-Ni-Al alloy as high strength and high conductivity materials.(2)In order to determine the direction and spontaneity of the reaction of Ni and Al atoms during the solidification of the Cu-Ni-Al alloy prepared by the melting method,thermodynamic calculations were performed.The formation of NiAl phase is caused by the most negative change of Gibbs free energy among all the potential reaction equations between Ni-Al system.The calculation results are consistent with the experimental results,which also proves the rationality of the calculation.(3)The hardness and electrical conductivity of the prepared three-component as-cast Cu-Ni-Al alloy were studied.The results show that the Ni and Al content decrease with the increase of Cu content,and The content of the Ni-Al precipitated phase in Cu matrix decreases,therefore,the hardness of the alloy gradually decreases;the wear rate of the alloy gradually increases,and the wear surface gradually changes from abrasive wear to adhesive wear.As the Cu content increases,the degree of solid solution of the Ni and Al atoms remaining in the Cu matrix gradually decreases,and the lattice distortion effect on the matrix is weakened,so that the electron motion hindering effect is weakened,and the electrical conductivity of the alloy gradually increases.(4)The Cu-5.4Ni-3.6Al alloy was subjected to solution treatment and aging heat treatment by orthogonal experiments.The analysis of the orthogonal results shows that:after solution treatment at 800?×4h and aging treatment at 450?×4h,Cu-5.4Ni-3.6Al can obtain the highest comprehensive performance,and has higher conductivity,hardness and tensile strength than the as-cast Cu-5.4Ni-3.6Al alloy.Therefore,the best heat treatment process is:solution treatment at 800?×4h and aging treatment at 450?×4h.