| Aluminum alloy has low density,good ductility and high specific strength.It is widely used in construction industry,aerospace,body components and other fields.However,due to its low hardness,poor wear resistance and low melting point,aluminum alloy is not suitable for high temperature,wear resistance and other application scenarios.High entropy alloy has the advantages of high hardness,good wear resistance,high temperature resistance and simple structure.From the perspective of performance,it is very suitable for surface modification of aluminum alloy.In this thesis,according to the characteristics of the large gap between the physical properties of aluminum alloy and high entropy alloy,using the design concept of gradient material,the gradient layer is prepared on the surface of 6061 aluminum alloy by laser cladding with Al Si10 Mg + Fe Co Cr Ni Mo high entropy alloy mixed powder with different mass fraction.The process parameters of preparing aluminum high entropy alloy gradient material by laser cladding on the surface of 6061 aluminum alloy were optimized.The univariate exploration test was carried out with the powder feeding amount,laser power and scanning speed as variables.The defects such as pores and cracks in the cladding layer and the surface average hardness under various parameters were compared to determine the final process parameters: the first gradient layer: powder feeding amount of 1.5 g / min,laser power 2100 W,scanning speed of 8 mm / s,ultrasonic power 1000 W Remelting power 2200 W,second gradient layer: powder feeding amount 1.5 g / min,scanning speed 7 mm / s,laser power 1900 W,remelting power 2000 W,third gradient layer: powder feeding amount 1.5 g / min,scanning speed 6 mm / s,laser power 2100 W,remelting power 2200 W.During the experiment,it is found that the laser energy density is too low,and feather like structures and intermetallic compounds are easy to form in the gradient layer,resulting in the cracking of the gradient layer.The microstructure and phase structure of each gradient layer were analyzed by OM,SEM and XRD.There is a single FCC phase in each gradient layer.The microstructure of the first gradient layer is mainly composed of slender columns α-Al dendrite and network Al Si eutectic,during which a small amount of eutectic Si precipitates;Fine petal like Al Si eutectic precipitated in the middle and upper part of the second gradient layer;The structure of the third gradient layer gradually forms fine dendrites from the coarse dendrites at the bottom of the cladding layer,and there are fine dendrites in the middle and upper part of the gradient layer.The Al Si eutectic precipitated at the junction of the first and second gradient layers presents a coarse dendrite,and ternary intermetallic compounds are formed at the junction of the second and third gradient layers.The microhardness,wear resistance and high temperature resistance of each gradient layer were tested and analyzed,and the temperature mutation point on TC /DSC curve was homogenized.The hardness test results show that compared with6061 aluminum alloy matrix,with the increase of high entropy alloy content,the hardness of each gradient layer increases by 6.59%,32.77% and 77.37% respectively;The wear performance test results show that compared with 6061 aluminum alloy matrix,the wear amount of each gradient layer is reduced by 13.04%,37.39% and80.86% respectively;The high temperature resistance test results show that the oxide on the surface of the third gradient layer is not continuous enough.Although the hardness of the samples after two groups of homogenization treatment is lower than that of the deposited samples,it is still 63.64% and 50.32% higher than that of the6061 aluminum alloy matrix respectively.The element distribution of the high entropy alloy in the gradient layer changes little,and it is still a single FCC phase without new phase,indicating that the gradient coating has good high temperature performance. |
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