| Spray forming has developed into a most important metal and alloy processing technology after undergoing universal investigation with the importance comparable with Ingot Metallurgy (IM) technology and Powder Metallurgy (PM) technology. Professor Cl-lEN Zhen-hua and academician HUANG Pei-yun in Central South University of Technology invented a novel spray forming technology termed as Multi-Layer Spray Deposition (MLSD) in 1995 which is different from the other similar technologies in principle. MLSD technology has been successfully utilized in the preparation of aluminum matrix composite reinforced with SiC particles. In this dissertation, the process principle of Multi-Layer Spray Co-Deposition (MLSCD) technology for preparation of aluminum matrix composite has been studied systematically. Based on this work and the improvement of experimental device and the optimization of process parameters, large-sized spray-deposited blanks of 6xxxAl/SiC~ composite with excellent quality have been produced, and serial conclusions have been drawn as follows:1. On the basis of the theoretic research on the traditional Osprey process, the particular heat-transfer and solidification laws of MLSCD were studied. The results of the numeric simulation analysis on present process show that MLSCD is a kind of rapid solidification technology with cooling rate reaching to iO~ ..4Oa ~ which is much higher than that in the Osprey process. In this process, it is the high thermal conduction from the atomized droplets to the solid-stated deposit surface that gives the rapid solidification effects. When they impact and splash on the deposit surface with relatively lower temperature, the liquid droplets are quenched and form thin layers with rapidly solidified dendritic microstructure. Meanwhile, the effects of two kinds of atomization nozzles and SiC injection methods on the heat-transfer and solidification characteristics of the MLSCD technology were also discussed.2. A comparative investigation on the capturing behavior of SiC particles injected into the atomization cone respectively with a dual-looped compound nozzle and injecting pipes were conducted. The results has shown that SiC particles injected by pipes can distribute more uniformly in the deposited layers than by a dual-looped nozzle, but its capturing percentage of the total amount of the injected particles is lower in the former process than that in the latter method. The main capture behavioriiin MLSCD is that the SiC particles impact and penetrate into the liquid dropletsduring the flying process. However, the deposit sdrice layer caPtUres SiC rarelybecause it is at solid state and at relatively lower temperat-Ure. Meanwhile, theoptimiZaion approach of process paraxneters to improve the caPthe effects anddistribution characteristics of SiC particles was obtained by theoretic analysis, whichwas proved by experimental results.3. A kind of pneumatic conveying system of SiC particles was designed, whichcan send out the reinforced particulate continuously and qUanificationally with ascrew mechedsm and a minus-pressured inhaling device. And the automatic controldevice and software system for controlling the scanning movement of the nozzle,diaxneter of billets and deposition distance was designed, by Which large-sized billetswith diaxneter deviation less than 4% can be prepared. On the basis of processparameters optirnZaion experiments, a 6066AnSiCp comPosite tube of size uP todo.,,r6 5 0/d l ..,3 00 x 8 00 nun and b il l ets o f size up to d6 5 0x6 0 0nun have been prepared,and exmided into large-sized tubular materials at one step. The mean grain size of theback-extrUded large 6066/l0%SiCp tube is smaller than 5ap, with fairly goodmechedcal properties reaching to or-23MPa, the-03MPa, 6 =3.6%, E=83GPa.
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