Preparation And Characterization Of Microstructure And Mechanical Properties Of 7075-t651/7075 Layered Aluminum Alloy Composite

Because the layered composite material can play the advantages of the component material and has a good overall performance,it has attracted much attention and has been more and more widely used.The solid-liquid compound method is a common method for forming a layered composite material.However,the dense oxide film on the surface of aluminum alloy is difficult to remove in time and effectively hinders the development and application of solid-liquid composite technology in layered aluminum alloys.Based on a large number of experiments,a device for preparing layered aluminum alloys composite was developed,and a 7075-T651/7075 layered aluminum alloy cimposite preparation technology,i.e.,impact jet continuous casting method was developed,and 7075-T651/7075 layered aluminum alloy composite was successfully prepared using this technology.The effects of various factors,such as the temperature of the casting,the velocity of the substrate movement,the delay time of the start of pouring and the start of the movement of the substrate on the bonding quality of 7075-T651 and 7075 aluminum alloys,were discussed.The optical microscope and scanning electrons microscope were used.Microscopy and XRD diffractometers were used to analyze the microstructure of layered aluminum alloy composite.The interface bonding state of the layered aluminum alloy composite was examined using an ultrasonic flaw detection instrument.The hardness of the layered aluminum alloy composite was measured using a rockwell hardness tester,an universal tensile machine,and a wear tester were employed to determine the mechanical properties such as strength and wear resistance.The results show that it is difficult to achieve the purpose of real removal of the aluminum alloy oxide film by using a stainless steel plate before casting to mechanically remove the film or chemically remove the lead.However,the use of impinging jet technology not only can completely remove the aluminum oxide film,but also can achieve a good bonding state between the aluminum alloy.Within the experimentally selected process parameters,the higher pouring temperature,slower substrate movement speed and slightly longer delay time contribute to the improvement of the bonding quality of the 7075-T651/7075 layered aluminum alloy composite within the selected process parameters.The best solid-liquid compounding process:the pouring temperature is 810°C,the moving speed of the substrate is 15mm/s,and the delay time is 5seconds.With this optimization process,the penetration depth can be controlled to about 10mm.The results show that the 7075-T651/7075 layered aluminum alloy composite was divided into five layers according to the microstructures and mechanical properties of the composite material:cladding layer,fusion line,heat affected zone I,heat affected zone II,and heat affected zone III.The cladding layer mainly consists of coarse Al dendritic structure;the fusion line is mainly composed of fine Al equiaxed grains;in the area adjacent to the fine equiaxed crystals appear preferential growth Al columnar crystals in the heat affected zone I,and the precipitated particles?'?MgZn?transition strengthening phase and T?Al₆CuMg₄?;Al grains in heat affected zone II become coarser,??MgZn₂?and a small amount of T?Al₆CuMg₄?phase are precipitated;in the heat affected zone III the microstructure characteristics of the 7075-T651aluminum alloy are similar to those of the original state,and the original precipitated??MgZn₂?strengthening phase is retained,but the grain size is slightly larger.The results further indicate that due to solidification of the aluminum alloy coating liquid in the coating process,more heat is transferred,resulting in the Rockwell hardness,tensile strength and wear resistance of the 7075-T651/7075 aluminum alloy composite layer and each zone decline to some extent.In the matrix alloy,the tensile strength at the fusion line is higher than that of the cladding layer.Combined with the microstructure analysis,it can be concluded that the metallurgical bonding is realized near the 7075-T651/7075 aluminum alloy fusion line.