| Hypereutectic Al-Si alloys are known to be suitable for wear-resistance material because of its low density, high tensile properties and low coefficient of thermal expansion. But the alloys fabricated by normal Ingot Metallurgy worsen the mechanical properties due to the coarse block-like or plate-like angular primary Si particles. Multi-Layer Spray Deposit (MLSD) technology is a kind of rapid solidification with high cooling velocity up to 1 04-1 06K/sec, which can improve the microstructure, lessen segregation and increase the solid-solution of the alloy.The thesis studies the processing, theory of MLSD technology making up the high silicon content Aluminum alloy, and also does research on the hot extrusion and the heat treatment of the alloy. The results are as following:1. The configuration investigation of plate, tube and billet made by MLSD technology shows: bigger of the value of ffly/cox, more complicated and not easier repeatable of the single footprint of spray. As the value of coy/cox is a irrational number, the single footprint almost not repeatable. The parameter is available for the uniform of the plate. Reasonably controlling the matching of the velocity of crucible, the rotation velocity of the substrate and the drawing velocity of the substrate can attain good-shaped tube. Matching the parameters of the offset of the substrate, spray angle, the velocity of rotation and the velocity of drawing of the substrate can make expected-shape billet, also increase the efficiency of the materials. The optimal parameters of making high silicon content aluminum alloys is: spray height is 220-230mm, spray angle is 30? the scanning velocity of atomizer is 30mm/s, the original offset of the substrate is 30mm, rotation velocity of the substrate is 120rpm, spray gas pressure is l.OMPa, the diameter of the delivery tube is 3.6mm, the drawing velocity of the substrate will be adjusted on-line with a PLC on the basis of the spray. The microstructure of as-deposit hypereutectic AI-Si-Cu-Mg alloy is composed of particulate-shaped Si particle and Equiaxed grain a-Al and few interstices. Due to the hijjji cooling rate of the MLSD technology, the primary Si is very fine and the distribution of Si phase is uniform. With the characterization of "Multi-layer" of MLSD, the relative density of the alloy is about 85-90%, little lower than that made by traditional spray forming. So the alloy should b ?densified on further.2. The room temperature tensile strength of alloy made by MLSD relate to the extrusion temperature and the extrusion reduction ratio, with high temperature and reduction ratio, the tensile strength becomes low. But the elongation is not sensitive tothe factors. So the temperature can be lower without lessen the elongation in the process of the extrusion process to get high tensile properties. The optimal extrusion parameters are as following: extrusion temperature is 375-400癈, the reduction ratio is 25:1.3. Investigation of heat treatment of the alloy shows the optimal heat treatment parameters is following: solid solution under 47CTC in 1.5 hours, then water quenched, artificial aging at 120癈. The disperse phase of alloy are MgiSk Al2Cu and AUCuMg. The aging curve demonstrated ''double peak". The cause of this phenomenon probably is Mg^Si phase dispersed first and then ANCu and Al2CuMg phase. The'peak time of alloy made by MLSD is 6 hours shorter than as-cast alloy, and the peak strength is up to 420MPa. The mechanical properties of alloy made by MLSD (ab=325MPa , CTs=307.8MPa, 5=3.2%) is superior to as-cast (ab=125.1MPa, crs=116.3MPa, 8=1.1%) mostly due to the very fine microstructure of matrix alloy and the uniform distribution of silicon particles. The abrasion cf the alloy is proportion to the friction distance. The alloy has good thermal stability; the fracture mechanism of the alloy is not obvious to Si particle size but closely relate t...
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