Study On Composition Design And Process Optimization Of Cu-Al Powder Alloy With High Strength And Wear Resistance

With the rapid development of modern industry,mining machinery,ships,aerospace and other fields have put forward higher requirements for the use of low-speed and heavy-load sliding bearings,but the existing bearing materials have been unable to meet the demand.Based on the idea of reverse design,this paper selected bearing materials according to demand orientation,and used machine learning to guide material design and process optimization.The sintering mechanism of Cu-Al powder alloy was studied,and the effect mechanism of the addition of different alloy elements on the microstructure and properties of the alloy were studied.The research content mainly includes the following aspects:(1)The working condition of low-speed and heavy-load sliding bearings was analyzed and the performance indicators for sliding bearings were obtained.Next,the diagram of the material properties was drawn using the Ashby approach,and Cu-Al alloy was selected as bearing material after comparison and screening.Finally,the powder metallurgy method was selected to prepare the sliding bearing materials.(2)The sintering and swelling mechanisms of the Cu-9A1 alloys prepared from elemental powders were investigated.The obtained results indicated that three consecutive layers of Al4Cu9,AlCu,and Al2Cu phases were formed between the Cu and Al particles at 480?,and Al2Cu appeared first.Eutectic liquid formed between the Al and Al2Cu phases at 500?,and the liquid phase infiltrated the gaps between the copper particles,leading to maximum swelling and a decrease in density.Above 565?,Al4Cu9 and ?-Cu transformed to AlCu3.The residual pure copper transformed to AlCu3,and the pore volume decreased at 1000?.(3)The prediction models of mechanical properties and sintering density of Cu-Al alloy were built using machine learning approach.Firstly,by comparing six models of tensile strength and hardness,the the sequential minimal optimization algorithm for support vector regression(SMOreg/puk)model had highest correlation coefficient and lowest error.The SMOreg/puk model was used to guide the composition design of the Cu-Al alloy such that its mechanical properties could attain the targeted values.Secondly,by comparing five prediction models of sintering density,the predicted value of the multilayer perceptron(MLP)model was consistent with the experimental value,and the maximum error value was lowest.The MLP model was used for the Cu-Al P/M alloy to guide the selection of the processing parameters to attain the expected sintering density.Finally,the Cu-12Al-6Ni alloy was prepared using the powder metallurgy method according to the composition and processing parameters,which were selected by the machine learning model,and a porosity of 11.22%,tensile strength of 390 MPa,and hardness of 139 HB were obtained.These parameters reached their expected values.(4)The effect of Ni content on microstructural evolution and properties of Cu-12Al powder alloy was investigated.The results indicated that the ?-Cu phase gradually increased,while the Al4Cu9 phase slowly decreased as the Ni content increased.When the Ni content was greater than 4wt.%,the NiAl phase precipitated at the grain boundaries.With the increasing of Ni content,the hardness of the alloy decreased gradually,but the strength of the alloy varied drastically.When the Ni content reached 6wt.%,the tensile strength and fracture strain reached the maximum,while the friction coefficient was the lowest.(5)The sintering behavior of the Cu-12Al-6Ni-xB(x=0,0.2)alloy was studied.The results revealed that pure Al disappeared,while large pores and a large amount of Al4Cu9 appeared in both alloys at 500?,and the sintering density of the alloys decreased sharply.At 600?,the martensite AlCu3 appeared in both alloys.At 700?,the Al4Cu9 phase and pure Cu of the alloy with B addition disappeared.At 1000?,the alloy with B had fewer pores and a finer structure.The effect of the B content on the microstructure and properties of the Cu-12Al-6Ni powder alloy was studied.When the content of B was 0.2wt.%,the microstructure of the alloy was apparently refined,and a large number of stacking faults and dislocations appeared in the microstructure.The sintering density,hardness,and tensile strength of the alloy with the 0.2wt.%B addition attained maximum values,respectively 91.7%,165.6 HB and 476 MPa,while the wear loss was the lowest.Upon increasing the B content,the sintering density,strength and hardness gradually decreased,while the friction coefficient and wear loss gradually increased.(6)The effect of Ti content on the microstructure and properties of sintered Cu-12Al-6Ni alloy was also studied.When 0.2wt.%Ti was added,the microstructure of the alloy was distinctly refined,and the granular X phase((Cu,Ni)2AlTi)appeared in the alloy.With increasing Ti,the X phase increased and coarsened,and pores appeared at the center of X phase.With increasing the Ti content,the tensile strength of the alloy increased initially but decreased subsequently.When the addition of Ti was 0.2wt.%,the tensile strength reached a maximum of 412.2 MPa,while the friction coefficient and the wear loss were the lowest.Upon increasing the Ti content,the friction coefficient and wear loss gradually increased.(7)The effect of graphite on the microstructure and properties of the sintered Cu-12Al-6Ni alloy was studied.On increasing the graphite content,the number of pores,Al4Cu9,and NiAl phases increased.The hardness and tensile strength of the alloy decreased as the graphite content increased,while the friction coefficient and wear loss increased first and then decreased.