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Studyon Microstructureand Property of Aluminum(Magnesium)Alloyvia Lost Foam Casting by Vibration Solidification

Author: PanDi
Tutor: FanZiTian
School: Huazhong University of Science and Technology
Course: Materials Processing Engineering
Keywords: lost foam casting ZL101 aluminum alloy AZ91D magnesium alloy mechanical vibration microstructure mechanical property heat treatment
CLC: TG249.6
Type: Master's thesis
Year: 2009
Downloads: 50
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Abstract

Aluminum alloy and magnesium alloy are widely used in the automotive andaerospace because of their merits including lower density, higher specific strength, betterheat conductivity, etc. And the lost foam casting (LFC) is suiting with forming ofaluminum alloy and magnesium alloy because of its advantages including natural gasshielding in pouring and filling, precision forming, clean production, and so on. However,the aluminum alloy or magnesium alloy via LFC has some disadvantages, such as largegrain microstructure, bad shrinkage porosity and shrinkage void, lower mechanicalproperties. These disadvantages have become the major barrier which limits the deeperapplication of aluminum alloy or magnesium alloy via LFC. In this thesis, the vibrationsolidification and vibration-pressure solidification technology were used for refiningaluminum or magnesium alloy grains and enhancing microstructure density to solve theproblem of insufficient mechanical properties. A new method of producing high-strengthaluminum or magnesium alloy via LFC was formed combined with the heat treatment.It had been researched that the effect of mechanical vibration on the microstructureand mechanical property of ZL101 casting sample via LFC. The results showed thatsuitable puring temperature was about 750℃because the casting sample possesseduniform microstructure, less shrinkage porosity or void, and better mechanical propertiesunder this temperature. Mechanical vibration could obviously refine the microstructure ofZL101 alloy via LFC comparing the normal casting condition. The casting had smallergrain size and lower pinhole rate by vertical vibration than the castings by other vibrationdirection. The effect of vibration solidification on the sample with different thicknessshowed that the more was the thickness, the more obvious was the vibration effect wouldbe got. The microstructure became finer as the frequency of vibration increased, whereasthe tensile strength and elongation percentage was enlarged first and then changed slowly.It had been researched that the effect of mechanical vibration on the microstructureand mechanical property of AZ91D casting sample via LFC. The results showed that theα-Mg primary phase was foundation, and the Mg17Al12 eutectic microstructure filled itdiscontinuously by mechanical vibration. The grain was tiny. The mechanical vibration could increase the mechanical properties of AZ91D alloy via LFC.It had been basicly researched the microstruture and propertities of aluminum alloyvia LFC under vibration-pressure solidification .The results showed that the grain ofZL101 was obviously refined by the effect of the mechanical vibration combined withpressure. The eutectic silicon in matrix distributed symmetrically. The sample wascomposed by equiaxed grain.This research selected simplex cylinder, pump body and supporting roller toaccomplish the pouring experiments by vibration-pressure solidification. The resultsshowed that vibration solidification combined with pressure on LFC had a strong ability ofmold filling. It could avoid misrun, cold shut, pinholes and weak performance whichusually appeared on aluminum alloy and magnesium alloy by general casting and goodcontour was attained.It had been researched that the effects on the microstructure and mechanical propertyof ZL101 casting sample via LFC, and the feasibility of semisolid heat treatment to ZL101casings via LFC. The results showed that the long needle-like eutectic silicon became shortstick-like or graininess, and the grain boundary separated outα-Si eutectic by T5 and T6.Itcould attained approximately intact globularity grain and the mechanical property wasimproved by semisolid heat treatment. When the temperature was maintained at 580℃for40min, the hardness was 94.2HBS and the tensile strength was 239.2MPa. As the soakingtime was too long, the grain would be crassituded, and the liquid phase would increase,then the sample would deform. The mechanical property of ZL101 casting sample via LFCwas better when the temperature was maintained at 580℃for 30~40min.

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