Influence Of Mn And RE Mischmetal On The Microstructures And Mechanical Properties Of AZ61A Wrought Magnesium Alloy

Currently, AZ61A magnesium alloys with low-cost are existence of inadequate toughness and low rate of extrusion processing. The microstructure, mechanical properties, forming ability of extrusion and corrosion property of AZ61A magnesium alloys through water cooling and mold cooling casting, homogenization heat treatment and hot-extrusion with different Mn and RE contents were investigated.The chemical compositions of all ingots were analyzed by Sparks Direct Reading Spectrometer, impurities in ingots were detected by Ultrasonic Flaw Detector, microstructure was analyzed by optical microscope and SEM (scanning electron microscopy), compositions and micro-zone composition of phases were analyzed by EDS (energy dispersive spectrometry), corrosion property was investigated by salt spray test. The research results indicated that:The distribution and morphology of theβ-phase were gradually changed from bulky irregular reticulation to small irregular reticulation to semi-continuous reticulation and to spot distribution with the ratio of Mn/RE decreased. With the increase of Mn and RE contents, the numbers and sizes of Al8Mn5 phase and Al4RE phase were increased respectively. Component 4 (Mn:0.68wt%, RE:0.67wt%) alloy has the best cast Microstructure.After homogenization as 420℃×10h, theβ-Mg17Al12 phase dissolved in the a-Mg phase and the segregation in the grain boundary was eliminated basically, Al4RE and Al8Mn5 phase with high melting point are remain in the organization. Composition 4 and composition 7 (Mn:0.30wt%, RE:1.0wt%) alloys'grain size are 100μm and 90μm respectively, which superior to the grain size of component 1 (AZ61A)alloy(180μm).The grain size of all alloys were refined by hot extrusion. Component 1(AZ61A) alloy can not be formed completely by hot-extrusion in the rate of 4.5m/min, other alloys in the coordination role of Mn and RE have good hot-extrusion property, and the grain size decrease first, then increase, and finally decrease, with the ratio of Mn/ RE decreasing. Extrusion electricity (equivalent to extrusion pressure) is increasing with the ratio of Mn/RE decrease.After hot-extrusion, tensile strength and yield strength of alloys that extrusion by separate extrusion rate are increase first and then decrease, the elongation decrease first and then increase, the corrosion rate were decreases first, then increase, and finally decrease, with the ratio of Mn/RE decrease. Composition 4 (Mn:0.68wt%, RE:0.67wt%) alloys that forming with the extrusion rate of 4.5m/min has good corrosion resistance and the corrosion rate is 0.068g/m2·h.Composition 4 (Mn:0.68wt%, RE:0.67wt%) alloy has get the intended purpose of the project, which with a substantial increase of extrusion speed (up to 4.5m/min), with appropriately extrusion pressure, good formability, low corrosion rate, and the tensile strength, yield strength are 281MPa,180MPa, elongation is 20%.