Study On Fabrication And Wear Resistance Of Sic_p/7075Composites

Aluminum matrix composites is attracting experts’ and practitioners’ attention inrecent years. Among them, the study about SiC particles reinforcement is verycomprehensive. In the actual production, ultra-high strength Al alloys of7XXX arevery popular because of their superior performance. Particulate reinforced compositewhose matrix is ultra-high strength Al alloys always use ospray now, but the studywhich aluminum matrix composite add SiCpby mechanical stirring has perfect.Output of composite products in ordinary state tend to be difficult to avoid defectshowever its organization or performance and on the material for further processing isalso a question which must consider in the production. Based on the aboveconsideration, this thesis carried out the following research.This thesis adopts mechanical stirring casting to prepare SiCp/7075composite;through the experiment, obtain the best process parameters which prepare thecomposite under the condition of the homemade mixing plant. The compositeprepared in500r/min,750℃and30min, whose SiC particles’ distribution is moreuniform and porosity and oxidation of defects are little and microstructure andmechanical properties are well, is best. The composite consists of α-Al, SiC and littlethe second phase. Most of the SiC distribute at the grain boundary. The nucleation andgrowth of the grain offer more resistance of SiC, so the grain’s size is smaller.In this thesis, the SiCp/7075composite has carried on the squeeze casting. Theplastic deformation which appeared in the squeeze casting process and is similar tothe appearance of the die forging will affect the whole solidification process. Theorganization will be more dense and defects almost disappeared. Grain is moreuniform than unsqueeze. Part of the SiC particles due to the effect of squeeze is pulled,spread further. The hardness of composite after squeeze increase by16.5%than10wt.%SiCp/7075composite and by37.9%than7075as-cast. These show theperformance of material has significantly improved after squeeze.In this thesis, the SiCp/7075composite has carried on the T6heat treatment. Through the experiment, the best obtained T6heat treatment parameters is465℃solution40min+130℃aging16h. Bimodal phenomena will appear in the process ofaging. Through the experimental results and analysis, the first aging peak precipitatedphase is GP zone which is coherent with matrix, which is precipitation strengthening.The second aging peak precipitated phase is T′(Al2Mg3Zn3) which is semicoherentwith matrix, which is dispersion strengthening. The interface between SiC and7075generates high density of dislocations, at the same time produces grain boundary, theinterface defects, etc, which will accelerate diffusion. So the composite achieves thepeak of the aging time which is shorter than7075alloy.This thesis also studied the wear behavior of SiCp/7075composite. When theparticle size is fixed, all materials’ wear rate will be increased with the increase ofload. The wear rate of squeeze casting composite after T6is better than other five as awhole. The wear rate of all will be increased with the increase of particle size. Thewear rate of squeeze casting composite after T6is although the best of all. Byanalyzing, the reason why squeeze casting composite after T6is better than others arethat T6heat treatment eliminate residual stress so that defects is difficult to appear;SiC particles on the surface of the matrix support the surface of the matrix and keep itfrom wear further; when squeeze is going on, squeeze pressure change thesolidification process of the material, the grains are refined, and compactness isstrengthened, all of which are good for suppressing abrasive particles embedding inthe matrix and preventing the furrows to expand.