The Effect Of Al And Si On The Structure And Properties Of Cu-Ni-Al(-Si)Alloy

As an important structural and functional metal material,copper alloy not only has high strength,high conductivity and high elasticity,but also has good wear and corrosion resistance,so it is widely used in many industries.With the development of high-end equipment in China,the demand for high-strength wear-resistant copper alloy used in marine atmospheric corrosion environment is increasingly urgent.The Cu-Ni-Al alloy has the characteristic of corrosion resistance,and the strengthening phase such as Ni3Al will be formed during the aging of the alloy due to the addition of Al element.Cu-Ni-Al alloy has the advantages of high strength,high corrosion resistance and high wear resistance,and is expected to be used in marine and atmospheric corrosion resistance components.In this thesis,Cu-14Ni-xAl alloy with 0,1%,2%,3%,4%,5%Al content was studied,and the heat treatment process parameters of Cu-Ni-Al alloy were studied.In addition,the effect of Al content on the microstructure and mechanical properties of Cu-14Ni-xAl alloy in peak-aged state was studied.On the basis of optimizing the content of Al,the effect of adding 0.5%～1%Si micronutrient on the microstructure and properties of Cu-Ni-Al alloy was further investigated.Based on the above experimental results,the relationship between alloy composition-microstructure-alloy properties is established.The research results indicate that the optimal aging temperature for Cu-14Ni-xAl alloy is 450℃.At this temperature,the aging precipitates in the alloy include fine dispersed granular precipitates within the grain and coarse rod-shaped precipitates at the grain boundaries.When the aging temperature further increases to 500℃,the precipitated phases in the alloy are suppressed.These precipitates are mainly concentrated at grain boundaries,weakening their strengthening effect on the alloy.The TEM experimental results indicate that the precipitates in the alloy at both the grain boundaries and the grain boundaries are Ni3Al phases with L12 structure.By studying the microstructure and properties of Cu-14Ni-xAl alloys with different Al contents,it was found that with the increase of Al content,the number of aging precipitates that can be obtained from Cu-14Ni-xAl alloy gradually increases,the size of precipitates also gradually increases.As the result,the hardness and conductivity of the alloy gradually increase.When the Al content reaches 2%to 3%,the precipitated phases in the alloy precipitate the most fully,and the hardness and conductivity also reach the highest.At this time,the wear amount of the alloy and the friction coefficient are also the smallest.T he friction coefficient is about 0.7.When the Al content further increases to 4%～5%,the intragranular precipitates in the alloy are suppressed,and the number significantly decreases.The precipitates are mainly concentrated at the grain boundaries,resulting in a decrease in the hardness of the alloy and a significant decrease in electrical conductivity,further leading to a decrease in the wear resistance of the alloy.Research has found that adding Al element to Cu-14Ni alloy can significantly improve the corrosion resistance of the alloy.This is because a dense oxide film is formed on the surface of the alloy during the corrosion process,and the three components of the oxide film,CuO,Cu2O,and Al2O3,can protect the substrate from corrosion.Within the range of 0～5%Al content,alloys containing 3%mass fraction Al have the best corrosion resistance.The effect of trace Si addition on the microstructure and properties of Cu-14Ni-2Al and Cu-14Ni-3Al alloys with better comprehensive properties was further studied.Research has shown that adding trace amounts of Si element can accelerate the precipitation rate of precipitates within the alloy grain,enable the alloy to quickly reach peak aging,and inhibit the precipitation of coarse and discontinuous precipitates at grain boundaries.On the other hand,after adding Si element,the alloy can generate Ni2Si phase during the aging process.Therefore,adding Si element can significantly improve the hardness and wear resistance of the alloy.The hardness of Cu-14Ni-2Al-1Si alloy reaches HV 323.77,and the friction coefficient is about 0.8.However,after the addition of Si element,the corrosion resistance of the alloy decreased.