Effect Of Composite Treatment On Solidification Structure And Properties Of In-situ Mg 2 Si/Al Matrix Composites

Aluminum matrix composites?AMC?has been widely studied and applied in various fields,because it is a new and high technology engineering material which is developed rapidly in recent years.In the process of preparing AMC,the properties of the final material are determined by the intrinsic factor and the interference of the external field.In this thesis,the effects of ultrasonic and added rare earth elements on the microstructure and properties of Al-18Mg₂Si-0.9Mg aluminum alloy were studied.The microstructure and mechanical properties of the composites were studied by T6 heat treatment.Finally,the wear properties of the AMC were tested.Firstly,the effect of La,Y,Sc and ultrasonic with different time and power on the primary phase Mg₂ Si and the microstructure of Al-18Mg₂Si-0.9Mg alloy were analyzed.The results show that the microstructure and mechanical properties of the composite materials with the addition of RE can be effectively improved in the Mg₂Si/Al matrix composites.The grain size of the primary Mg₂ Si particles is first decreased and then increased under different the ultrasonic power and the same time.At the ultrasonic power is 150 W,the particle size is 18.40 ?m.The tensile strength and elongation of the best Mg₂Si/Al matrix composites were improved by 111.9% and 98.02%,respectively.The grain size of the primary Mg₂ Si particles is first slightly increased and then decreased under different the ultrasonic time and the same power.At the ultrasonic time is 40 s,the particle size is 36.38 ?m.The tensile strength and elongation of the best Mg₂Si/Al matrix composites were improved by 139.29 % and 178.71 %,respectively.The solidification structure of Mg₂Si/Al matrix composites was significantly changed after the addition of La to the ultrasonic treatment compared with no addition of rare earth La for ultrasonic treatment.At the ultrasonic power is 150 W,the hardness is 132 HB,the tensile strength is 201 MPa,the elongation is 5.28%.Secondly,the structure and properties of Mg₂Si/Al matrix composites under different conditions were studied in different time of solution and aging treatment.The results show that the microstructure and hardness of the composites were effectively changed at different T6 treatment.The morphology and size of the primary Mg₂ Si of the composite were significantly changed at the different solution time and the aging same time.The size of the primary Mg₂ Si particles decreased significantly in the early stage of solid solution treatment.The composite material is close to the saturated state when the size decreases slowly.At this time,the hardness of the composite material is first increased and then decreased.The morphology of the primary Mg₂ Si of the composite were significantly changed and the size of little changed at the different aging time and the solution same time.The sequence of the precipitation phase of the general Mg₂Si/Al matrix composites is that the ? saturated solid solution,the atom cluster,the GP region,?”,and the ?'phase transition phase,the stability of the ? with the increase of aging time.Similarly,the hardness is first decreased and then increased of the composite material.Finally,the friction and wear tests of the Mg₂Si/Al matrix composites without T6 heat treatment were carried out under different friction force.At the same time,the friction and wear behavior are discussed.The results show that the wear resistance of Mg₂Si/Al matrix composites under different processing conditions is better than that of conventional gravity casting composites.The wear resistance of Mg₂Si/Al matrix composites is related to two aspects.On the one hand,the wear resistance of the composite is determined by its hardness.On the other hand,the wear performance is related to the microstructure of the composite material.The wear rate of the material increases with the increase of the friction force is found by using different friction forces in the process of friction and wear of the composite materials of La and ultrasonic.