| The 7075 aluminum matrix composites reinforced with 0-10wt.% nano-Al2O3 particles were fabricated by high energy ball milling and hot press sintering. The microstructure, room temperature mechanical properties, friction and wear behavior of the composite material at different temperatures were studied. The microstructure of the composite material was analyzed by XRD, SEM and TEM, and its mechanical properties were tested by brinell hardness and electronic universal testing machine. The appropriate ball milling and hot press sintering process parameters were determined by the test results. The effects of different equal channel angular pressing (ECAP) processes on microstructure and properties of hot pressed 7075 aluminum alloy and 5wt.% Al2O3p/7075 aluminum matrix composites were studied and the best ECAP process were also determined. Friction and wear properties of 7075 aluminum alloy and 5wt.%Al2O3p/7075 aluminum matrix composites at room temperature to 200 ℃ were analyzed, and the friction and wear mechanism was explored by combining analysis of the friction coefficient, wear rate and worn morphology. The main conclusions were as follows:The investigation of the high energy ball milling process showed that when the milling speed was 350r/min and the ball to powder ratio was 20:1, after ball milling for 20h, the morpholgy of the composite powder tended to equiaxed, cold-welding and fracture reached balance. With the increase of sintering temperature, the hardness and density of 5wt.% Al2O3p/7075 aluminum matrix composites showed a trend of first rising and then falling, and the hardness and density reached the maximum at 620 ℃. After hot press sintering at 620 ℃, the density of Al2O3p/7075 aluminum matrix composites with different mass fraction of nano Al2O3 reached above 90%. The study on the microstructure of nano Al2O3p/7075 aluminum matrix composites showed that with the content of nano Al2O3 particles increasing, the grain size of the composites was obviously refined, and the density decreased gradually. When the Al2O3 content was 5wt.%, the distribution of the reinforced phase was more uniform with no obvious agglomeration. With the increase of the content of nano Al2O3 particles, the elongation of the composite gradually decreased, the hardness and tensile strength first increased and then decreased. When the Al2O3 content was 3wt.%, the hardness and tensile strength of the composite reached maximum of 205.7HB and 297MPa respectively. Fracture mode of 7075 aluminum alloy without nano Al2O3 particles was ductile fracture. Whereas, after adding nano Al2O3 particles, the fracture mode of the composite was cleavage fracture.With the increase of extrusion temperature, the tensile strength of 7075 aluminum alloy increased at first and then decreased. However, the elongation of the alloy decreased at first and then increased. The appropriate ECAP temperature of 7075 aluminum alloy was 250℃. With the increase of ECAP passes, the tensile strength of 7075 aluminum alloy increased obviously, and the elongation decreased at first and then increased. The density, hardness and tensile strength of the alloy increased obviously with the increase of the extrusion passes. Compared with the hot pressed composites, after 2 passes at 450℃, the distribution of nano particles of 5wt.%Al2O3p/7075 aluminum matrix composites was more uniform, and the density, hardness, tensile strength and elongation were also improved.The study on the friction and wear performance of composites showed that the wear properties of the composites were significantly improved by the addition of 5wt.% nano Al2O3 particles. However, the effect of ECAP deformation on the wear properties of the composites was not obvious. With the temperature increasing, the friction coefficient and wear rate of 7075 aluminum alloy and Al2O3p/7075 aluminum matrix composite increased, but the wear rate of the composites was significantly lower than the 7075 aluminum alloy. Especially at 200 ℃, the wear rate of composites was about 1/10 of the 7075 aluminum alloy. At room temperature and 100℃, the wear mechanism of 7075 aluminum alloy was mainly abrasive wear, oxidation wear and adhesive wear, and the wear mechanism of nano Al2O3p/7075 aluminum matrix composites was mainly abrasive wear and oxidation wear. Whereas when temperature increased to 200 ℃, the wear mechanism of 7075 aluminum alloy was delamination wear, but for nano Al2O3p/7075 aluminum matrix composites, the wear mechanism was adhesive wear. |
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