| The strength of Cu-15Ni-8Sn alloy is produced by controlled thermal treatment that causes spinodal decomposition.Its excellent properties include high strength,high elasticity,excellent friction resistance,stress relaxation resistance and corrosion resistance.As a potential substitute alloy for beryllium bronze,it has considerable market application value in many fields.The main problems of Cu-15Ni-8Sn alloy are the inhomogeneity of the composition during solidification and the discontinuous precipitation growth during the aging process,which greatly weakens the properties of the alloy.In order to solve the problems mentioned above,this paper adds the fourth component Mg to the Cu-15Ni-8Sn alloy and changes the casting mold to carry out related experimental studies under different conditions of the alloy.The main contents are as follows:Firstly,after adding different Mg content to Cu-15Ni-8Sn,the existence form,effect and mechanism of Mg element are studied.The as-cast structure of Cu-15Ni-8Sn-x Mg alloy is coarse dendrites,and Mg tends to combine with Sn and is dissolved in the Sn-rich phase and discontinuous precipitation.After being held at 850?for 4h,Mg was completely dissolved into the alloy matrix.The alloy becomes a single-phase supersaturated solid solution,and Mg can enhance the solid solution strengthening effect of the alloy but reduce the electrical conductivity of the alloy.The aging treatment is carried out at a temperature of 400?.With aging time increasing,discontinuous precipitation formed at grain boundaries of the alloy continues to grow;Mg element can inhibit the growth of discontinuous precipitation,and the more the content is added,the stronger the blocking effect is.The aging hardening curves of Cu-15Ni-8Sn-x Mg alloys all show a single peak.And a large amount of discontinuous precipitation causes a rapid decrease in the hardness of the alloy.But the hardness of the alloy with 0.3wt.% Mg is basically unchanged after reaching the peak.The hardness and conductivity of the alloy with 0.3wt.% Mg after aging at 400? for 6h are 369 HV and 8.37%IACS,respectively.When aging for 10 minutes at 700?,continuous precipitation phase and discontinuous precipitation phase will be formed in the alloy at the same time.At this time,Mg still has an inhibitory effect on the growth of discontinuous precipitation,and Mg element can promote the formation of continuous precipitation.Cold rolling deformation can accelerate the formation of discontinuous precipitation structure in Cu-15Ni-8Sn and Cu-15Ni-8Sn-0.2Mg alloys,and advance the alloy peak hardness time.The electrical conductivity and peak hardness of the alloy increase with the increase of deformation.In addition,the as-cast structure of Cu-15Ni-8Sn alloy is significantly refined by changing the casting mold,and the composition distribution is more uniform.The uniform distribution of Sn and the refinement of the structure make the growth of discontinuous precipitation of Cu-15Ni-8Sn alloy slow down when aging at 400 ?;when aging at 700 ?,continuous precipitation is uniformly formed in the alloy matrix;The hot rolling cracking tendency of Cu-15Ni-8Sn alloy with refined grains at850? is significantly reduced. |
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