Mg-Al alloy cast structure refinement techniques for basic research

Title: Mg-Al alloy cast structure refinement techniques for basic researchAuthor: Gao DemingDegree-granting units: Shanghai UniversityKey words: magnesium alloy;; cast structure;; grain refinement;; ultrasound;; magneto-oscillations;; pulse currentSummary:Magnesium alloys have high specific strength, specific stiffness, good damping, thermal conductivity and machinability widely used in automotive, electronics, aerospace and other fields. Improve the strength of magnesium alloy and plastic deformation, in order to expand its scope of application, materials, workers in recent years become the goal. Grain refinement is to improve the mechanical properties of magnesium alloys the most effective methods, so grain refinement of Magnetic lifter magnesium alloy technology has great significance.In this paper, orthogonal experimental study of Al, Zn, Mn three kinds of alloying elements on the suction-cast magnesium alloy mechanical properties of the law, the results show, Al content in Mg-Al alloy affect the mechanical properties of the key factors, Zn, Mn impact of changes in the relative content of Al in terms of weak. In this paper, conditions, Mg-6Al-0.6Zn-0.3Mn for the suction-cast magnesium alloy the best ingredients.The use of vacuum suction casting method to study the Ca, Ce content on Mg-6Al-0.6Zn-0.3Mn alloy cast structure were investigated. Experimental results show that, Ca, Ce-cast the alloy has a significant thinning effect: When the amount of Ca added in the range 0 to 0.9%, with the Ca content increases, the grain size decreases; when Ce Add the amount in the range 0 to 1.0%, with the increase in the amount of Ce, are becoming increasingly well-developed dendrites, http://www.999magnet.com/products/131-magnetic-lifter dendrite arm necking phenomenon intensified, which showed off a small rod-like grains gradually increased, the grain boundary on the β-Mg17Al12 phase decreased, but there is a new phase Al4Ce;By high temperature liquid quenching experiments and thermal analysis techniques to study the Ca and Ce on the Mg-6Al-0.6Zn-0.3Mn alloy solidification process of the impact mechanism. The results show that, Ca promoted the liquid core in the heterogeneous nucleation, dendrite growth inhibition of α, so that the magnesium alloy equiaxed size decreases; Ce magnesium alloy to promote dendrite growth, thereby inhibiting the magnesium alloy dendrite cutting-edge nucleation. Analysis, Ca enrichment during solidification solid-liquid interface on the front, ahead of the interface increases the undercooling of the liquid phase, thus contributing to cutting-edge liquid interface in the heterogeneous nucleation, and inhibit the first analysis of the grain grow up; Ce during solidification at solid-liquid interface adsorption, reducing the interfacial energy, thus contributing to the growth of dendrites, which leads to cutting-edge liquid interface undercooling decreases, the inhibition of the differences in the liquid phase ahead of the interface nature of nucleation, reduces the secondary dendrite α dendrite spacing.In the Mg-9Al-0.8Zn-0.3Mn alloy solidification process using ultrasonic, magneto-oscillation and pulsed current and other physical processing, and modification with MgCO3 the results were compared. The results showed that power ultrasound on the alloy-cast significant refinement, with the increase in power, refinement is more effective when the power reaches 500W, its refinement than MgCO3 modification better. Magneto-oscillations of the cast structure of alloys has also been significant refinement, and with the magneto-oscillation voltage increases, the thinning effect is more obvious, when the voltage reaches 100jV or more refinement than the better modification MgCO3 . Pulse current of the cast structure of alloys with the same refinement as the pulse current and voltage increases, the thinning effect increases when the voltage reaches 250jV MgCO3 when refinement and modification are quite effective.Analysis of different physical fields and MgCO3 modification of the cooling curve shows three kinds of physics dealing with the initial solidification temperature of the alloy is less, but can significantly shorten the solidification time; and MgCO3 Modification initial solidification temperature of the alloy was increased coagulation time slightly shorter. Analysis, the main external physical field through the promotion of melt heat treatment and increase the type of wall and drift off nuclei, thus contributing to its solidification structure refinement; and MgCO3 major modification of heterogeneous nucleation by increasing the particle.Degree Year: 2009