Effects of the Superheating Temperature and the Cooling History on As-cast Microstructure of AZ Series Magnesium Alloys
|Course||Materials Science and Engineering|
|Keywords||AZ series magnesium alloys Overheating Treatment Dendrite arm spacing Micro- component analysis|
Small uniform tissue magnesium alloy slab, thermal processing and cooling process in the process of casting magnesium alloy solidification structure of the shadow - rang regularity and mechanism study. Used AZ31 of AZ61, AZ91 alloy using melting - solidification method, by controlling the melt temperature, the cooling rate of the different microstructural by optical microscopy, scanning electron microscopy and spectroscopy analysis of alloy solidification organizational structure and micro ingredients, alloy hardness, micro hardness tester test to identify melt superheat, cooling history of organizational performance on the slab and Al, Zn alloy elements of composition distribution were investigated. The main contents include: the overheat temperature on different aluminum content of the AZ series alloy cast microstructure and microhardness; cooling history of the AZ series magnesium alloy cast microstructure dendrite and secondary dendrite arm spacing and microhardness investigated. AZ31, AZ61 and AZ91 alloys, respectively, by the maximum heating temperature of 750 ° C, 800 ° C, 850 ° C, 900 ° C and 950 ℃ of overheating treatment, the results show that with increasing Al content, AZ series magnesium alloy cast Organization primary dendrite arm spacing and secondary dendrite spacing the shorter secondary dendrite dense, alloy microhardness increase, more uniform microhardness. Processed by different superheat temperature solidified alloy, Al, Zn element concentration to time from crystallization center dendrite gap along the radius direction of the primary dendrite is gradually increased, with the increase in the degree of superheat, the cast microstructure primary dendrite spacing and the secondary dendrite arm spacing, composition segregation weakened microhardness increase. Organizations and reduce component segregation for refinement, the AZ series overheating temperature of 900 ° C. AZ61 alloy in high temperature melt phase solidification stage and solidification stage of completion using different cooling rates obtained solidification structure study to compare the dendrite arm spacing and microhardness results show that the high-temperature melt phase cooling rate of change of cast state organizations. Using the statistical method of fitting the empirical formula of the interdependence between dendrite arm spacing and secondary dendrite arm spacing and cooling rate, the empirical formula is as follows: primary dendrite arm spacing and cooling rate of AZ61 solidification stage relationship: y = 121.04 secondary dendrite arm spacing and cooling rate in the x-0.2618AZ61 solidification phase relationship formula: y = 10.682x-0.0799AZ61 solidification completed stages of the relationship of the primary dendrite arm spacing and cooling rate: y = 122.81x-0.2033AZ61 solidification completed Phase II secondary dendrite arm spacing and cooling rate relationship: y = 9.8276x-0.1079 This paper studies overheating treatment temperature and cooling historical process slab AZ series magnesium alloy microstructure impact, in addition to the analysis of dendritic morphology, dendrite arm spacing and microhardness values ??and other conventional means, but also to establish a different distribution than the alloy composition of the dendrite characteristic microscopic area, cast as a measure of state organizations compositional uniformity standards. Its contrast range, including matrix dendrite, dendrite branches, secondary dendrite branches, secondary dendrite gap and a dendrite gap five regional studies prove to have some value in use.