The Effects Of The Squeeze Casting Process Parameters And Refining Methods On The Microstructure And Properties Of AZ91Magnesium Alloy Containing2%Y

AZ91magnesium alloy which is an excellent cast alloy is widely used for its highspecific strength, specific stiffness and good electromagnetic shielding. However, its poormechanical properties, corrosion resistance, heat resistance and its inflammability limit itsfurther application. Therefore, It’s important to improve the magnesium alloy’s mechanicalproperties for its application. Squeeze casting is a near net forming technology by which themolten metal fills the mold at low speed, its formation and solidification are completed athigh pressure. A little plastic deformation occurs in the castings. So the castings can obtainimpact structure and have no shrinkage cavity and shrinkage porosity defects. The squeezecasting is an effective method which can improve the overall performance of the casting.The effect of the squeeze casting process parameters （pouring temperature, extrusionpressure, mold temperature, dwell time） and the solution-aging treatment on the structure andmechanical properties are investigated by orthogonal experiments using the stretch andhardness tests, metallographic test, SEM, EDS and XRD diffraction analysis combined withthe2%dosage of the rare earth Y.The results are as follows:（1） The biggest effect factor of squeeze casting process parameters is the moldtemperature, pouring temperature is in the second place, the squeezing press is the third, dwelltime is the last for the tensile strength, elongation, squeeze pressure and Brinell hardness ofthe AZ91magnesium alloy containing2%Y.（2） The biggest values of tensile strength, elongation, Brinell hardness of the specimenare185.48MPa,5.2%,84.9HB, respectively obtained by the test results.（3） The tensile strength and the elongation can be improved by the solution-aging treatment significantly, but the Brinell hardness decreases. The tensile strength and elongationincrease by33.5%and142.3%, respectively.（4） Extruded grains of the specimen is smaller than others under the optimal processparameters. The coarse β-Mg17Al12grains at the boundary can be eliminated, the distributionof the grains are more uniform and more Al2Y phase precipitated under the solution-agingtreatment.（5） There are fewer river patterns and clesvage steps in fractograph of extrudedspecimens. The fractograph of the specimen is obviously river pattern under the solution-aging treatment. There are many tear ridges, tiny clesvage steps and dimples in the fracture.The fracture is fibrous and the structure is compact. Apparent necking is occurred in thespecimens.The inclusion and the hydrogen absorption are the factors which can affect the propertiesof magnesium alloy. The refining is the effective method to remove them. The effect on theAZ91magnesium alloy containing2%Y of different refining methods are studied in thispaper. The results are as follows:（6） The best mechanical properties is the case of adding refining. The second is the caseof blowing Ar rotatably. The worst mechanical properties is the case of no refining.（7） The tensile strength of the extruded casting is improved, but the Brinell hardnessdecreases slightly in the case of adding the refining and blowing Ar rotatably.（8） The grains under heat treatment is bigger slightly than that without heat treatment.The distribution of grains is more uniform. The β-Mg₁₇Al₁₂phase at the boundary dissolveinto α-Mg basically. The Al₂Y phase is precipitated uniformly. The fractograph is river pattern,there are many tear ridges and tiny clesvage steps in the fracture and the structure is moreimpact under the heat treatment.