Study On Microstructure Of Mg-9Al Magnesium Alloys About Different Zn Content

By tensile tests using optical microscopy,scanning electron microscopy and universal mechanical testing equipment and other metho,properties and microstructure of Mg-9Al-xZn (x=1,3,5wt%) alloys and semi-solid organization were conducted and studied. The variation of the total composition, microstructure and properties were analyzed. The alloy cast and semi-solid state phase transition were explored.And it is discussed that in the next semi-solid, alloy composition, holding time and holding temperature influence law to the semi-solid organization. It is indicated that the main study phases were a-Mg phase, β-Mg17Ali2phase, y-Mg32(Al, Zn)49phase and Mg-Zn phase. Alloy grain for typical dendrites, eutectic phase distribution in grain boundary, along with the increase of the content of Zn, branch grain size and distribution were more diffuse.Using the universal mechanical testing machine to measure alloy Mg-9A1-Zn was184MPa, alloy Mg-9Al-3Zn tensile strength was192MPa, alloy Mg-9Al-5Zn tensile strength was204MPa, and with the increase of the content of Zn alloy tensile strength in increased. And with the increase in Zn content, the hardness of the alloy also showed an increasing trend. In the experimental study of heat treatment system, it is showed that:Under the condition of the heat preservation time is constant, with the increase of heat preservation temperature, the semi-solid dendrite globular group of grain size decreases first, after the basic remains the same, to further improve in the temperature of the heat preservation, get all the liquid, solid ball organization disappear. In a certain temperature range, solid rate is gradually reduced, the roundness of the grain is improved. In the insulation under the condition of constant temperature, as the extension of heat preservation time, semi-solid non dendritic crystal ball organization of solid gradually reduced, the roundness of the grain size gradually increased and grain size was reduced. Generally, when holding time after more than45min, grain size began to increase. In9Mg-Al-xZn alloy, along with the increase of the content of Zn, alloy grain size is gradually reduced, namely the semi-solid dendrite globular group gradually become dispersion tiny. In the temperature of570℃, under the condition of heat preservation for30min, the semi-solid non dendritic structure is best, the particle size of Mg-9A1-Zn was74μm, the particle size of Mg-9Al-3Zn was68μm, and the particle size of Mg-9Al-5Zn was57μm.