Preparation And Study On Wear Resistance Of Mg₂Si/Fe-rich Recycled Aluminum Matrix Composites

Aluminum alloys have been widely used in automative,aerospace,3C industries and other fields because of their excellent characteristics,such as low density,high specific strength and excellent corrosion resistance.Recovery and utilization of scrap aluminum has become an inevitable choice for the sustainable development of aluminum industry with the market saturation of aluminum comsuption.High content of impurity Fe and its removal from the Al melt are the main challenges of high-quality utilization for recycled aluminum alloys.Based on this problem,a novel route was porposed in the present study that recycled alumimun alloys with high Fe content was chosen as metal matrix of compoites reforced by Mg2 Si particles.The Mg2 Si phase is formed by reaction Mg and Si in Al melt during solidification.The contents of the Mg2Si/recycled A356 aluminum matrix composite were optimized.The vibration casting was utilized and the Fe-rich phase was modified to improve the microstructure and mechanical properties of the compostes.Finally,the wear property was systematically studied.Some conclusions were obtained as follows:The researches of impurities content in recycled aluminum alloys based many data from factories shows that the average content of impurity Fe in recycled aluminum alloy is about 0.67% and part of recycled aluminum alloy Fe content is as high as 1.2% which is much higher than corresponding commercial aluminum alloys.The contents of Mg2Si/recycled A356 aluminum matrix composites ware optimized based on wear resistance.The optimal Mg2 Si and Fe contents were 15% and 1.5%.The composite was named as 15%Mg2Si/recycled A356-1.5Fe.The rich-Fe phase could be effectively modified by combination of elements Mn and Cr from needlelike β-Fe phase to nodular and rod like α-Fe phase.Better modification effect could be obtained when the Mn and Cr addition contents both were 0.5%.Based on 0.5%Mn/0.5%Cr combining additions,RE or Sr addition could not be further to improve the modification effect.The solidification and crystallization sequence of the 15%Mg2Si/recycled A356-1.5Fe composites system was as following: primary Mg2 Si phase(649.8℃)、β-Fe phase(629.8℃)、 π-Fe phase(618.3℃)、 Al+Mg2Si binary eutectic(578.3℃)and Al+Mg2Si+Si ternary eutectic(556.7℃).The solidification and crystallization temperature of α-Fe phase in the composited modified by 5%Mn/0.5%Cr combining additons was higher than β-Fe phase that in the compostes without modification.The systematic wear test result shows that wear resistence of 15%Mg2Si/recycled A356-1.5Fe matrix composites modified by 0.5%Mn/0.5%Cr was obviously better than that of recycled A356 alloy.The critical transition load from mild wear to severe wear of recycled A356 alloy was in the range of 250~300N.However,no severe wear occurred for the 15%Mg2Si/recycled A356-1.5Fe matrix composites within the scope of the test load when sliding speed was 214r/min.The critical transition load was improved from 150~200N to 200~250N for the recycled A356 alloy and composites when sliding speed was 428r/min.The worn surface shows that the wear mechanism of recycled A356 alloy and composites under different test condition below critic trasition loads mainly exhibited abrasive wear and oxidation wear.With increasing of applied load and sliding speed,abrasive wear and oxidation wear become severe.The alloy body was softened because of high friction temperature which leads to severe wear occurred with applied load above critic trasition loads.The friction temperature result shows that composites could still maintain stable wear when friction temperature was as high as about 200℃.However,sever adhesive wear occurred for the recycled A356 alloy when friction temperature was only about 160℃.The advantage of wear resistance of composites is more obvious than recycled A356 alloys under high applied load and high sliding speed.