| Magnesium alloy has developed to magnesium matrix composites for the limitation of its machanical properties.In recent years, friction stir processing technology which develop from friction stir welding attracts more and more general research scholars' attention.It has unique advantages:its solid-phase processing can obviously cut down metal hole,compact organizational structure and refine grain greatly.Therefore,manufacturing magnesium matrix composites by friction stir processing method has important research significance.Besides,the choice for reinforcement also transfer from microns to the nanometer level gradually, limitations of the single reinforcement make more scholars begin to expand their research into matrix reinforced composites.From that point,this thesis presents the manufacture of nano-sized Al2O3 and CNTs hybrid reinforced AZ31 magnesium matrix composite by friction stir processing technology.This thesis mainly research the impact on structure and properties of the composites with FSP,load,the change of content of nano-sized Al2O3 and CNTs,also to understand the wear friction behavior, wear mechanism and hybrid effect in detail.The conclusions are follows.The best technological parameter of FSP is as follows.Rotata speed is 1050r/min,cutting speed is 33.4mm/min,and the number of FSP is four.The composite material by FSP has no obvious defects.The enhanced evenly distributed in the matrix without obvious piles of aggregation well combined with the matrix.The study shows:the wear resistance of magnesium alloy with FSP is better than the wear resistance of magnesium alloy without FSP.Compared with the two magnesium matrix composites reinforced with single particulate, the magnesium matrix composites reinforced with CNTs is better.And the wear resistance of the matrix reinforced composites is superior to the single reinforced composites.The change range of the wear loss of material is very gentle with the increases of the content of nano-sized Al2O3 under the 0.65MPa to 1.30MPa.Thus,the impact of the content of nano-sized Al2O3 on mixed composite materials is not big,but under load in the range from 1.95MPa to 3.25MPa, the change range of the wear loss of material is large with nano-sized Al2O3 increases,with the phenomenon of greatly increase or decrease.When the content of nano-sized Al2O3 is 30%,and the content of CNTs is 70%,hybrid synergy between them achieve the best, and the wear resistance of composites hybrid reinforced with them is the best.The preliminary analysis showed that the weight of wear exhibited different regions, therefore,the wear should be controlled by different wear mechanisms. In the case of low load, the wear surface is smooth with no obvious pears ditch, and has small debris. The EDS patterns of worn surface of the composite indicated that the worn surface is covered by mechanically mixed layer composed by the oxides of Mg, Al, Cr, Fe, the wear mechanism at this time is oxidation wear. With load increases, the transferring layer disappear,there are wide and deep plough groove,at the same time the worn surface shines,so grain wear mechanism at the stage. In the case of high load, the main wear mechanism of hybrid reinforced composites is delamination wear of the mechanical mixed layer. Black film exhibit in the region of friction surface and increasing with the increasing of loading.So,the existance of mechanically mixed layer has some influence on the wear properties of composites. |
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