Process Of Scanning Spray Forming And Analysis Based On As-Deposited Microstructures Of Magnesium Alloy

In this paper, design concept and structural characteristics of double-layer scanning atomization has been illustrated. Making use of the flexibility of the Four-bar linkage structure and the lower open atomization, the swing of the atomization has been achieved, furthermore the shadow area of the atomization cone increased more than doubled, it will be suitable for preparing larger spray-formed billet. In the aerodynamics experiment, assembly parameters of double-layer scanning atomization had been determined. Protrude length of the delivery tube in the top atomization is 6mm, and the distance between the top atomization and the lower atomization is shorter than 40mm.Spatial distribution changes of droplets density have been considered in the paper, and then a mathematical method tracing the coordinate of the surface of the spray formed billet has been utilized, the model for the prediction of billet shape geometry has been established which adapt to the atomization without the scanning atomizer and the atomization with the scanning atomizer. Using this model, the shape and size of the spray forming billet is predicted under vary spray forming technological conditions, and the effects of the spray forming parameters for example off-center distances,spray angel,moving speed of disc,scanning angel of atomizer are analysed. The moving speed of disc plays greatly roles on the diameter and height of the spray forming billet. The Faster speed of the disc, the thinner and higher the billet is formed. The scanning atomizer can eliminate the pit in the top of the billet.The microstructure of the as deposited Mg-Zn-Zr alloy and the powder were observed by OM and SEM in the paper. The phase composition of the as-deposited Mg alloy was analysed by XRD. The shape of over-spray powder is sphericity, and the diameter of the powders is less than 50μm. The freezing rate of larger powder is slower than the smaller one's, furthermore the distance between neighbor secondary dendrite is farther in the larger one. The density of the as-deposited Mg alloy isn't uniform, the max density reaches to 98% of the theory density, while the min density is less than 90% of the theory density. The characteristic of uniform equiaxed grains was observed in the as-deposited microstructure of Mg alloy, the average size of the grains is about 20μm. The as-deposited microstructure is greatly refined comparing with the as-cast state. the top and the below microstructure of the longitudinal section of the spray forming billet are similar, but there are pores inside of the billet. The matrix of as-deposited Mg-alloy isα-Mg, in which some Zn is dissolved. XRD diffraction confirms that there are some Mg2Zn3 in the matrix. Zr is detected in the precipitates which distribute along the grain boundary and in the grain.