Weihong Li

Protective Ability of Graphite Powder on Molten AZ91D Magnesium Alloy

Graphite powder was used to prevent a molten AZ91D magnesium alloy from oxidation and burning in order to develop a new pollution-free protection method with low cost. The protection method is expected to have good protective effect without decreasing the mechanical properties of the alloy. The protective ability of graphite powder on the alloy was investigated. Experimental results showed that graphite powder could protect AZ91D melt. The protective ability increased with graphite powder amount and decreased with holding time. The microstructure, chemical composition and phase composition of the surface films formed on the molten AZ91D alloy were analyzed using scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction, respectively. The protection mechanism was discussed. The surface films produced by the reactions between graphite powder, AZ91D alloy melt and the ambient atmosphere had two layers. The continuous and compact outer layer, mainly consisting of MgO and C, may be the fundamental reason for the fact that graphite powder could protect AZ91D alloy melt.

Effects of Al-Ti-B-Sr Master Alloy on the Microstructure and Mechanical Properties of A356 Alloy

A356 alloy was refined with a new master alloy of Al-5Ti-B-10Sr. The microstructure and mechanical properties of the refined A356 alloy with different content of master alloy (0, 0.1, 0.3, 0.5 and 0.7 wt.%) were investigated. The results show that the refining effect becomes stronger as the master alloy content increasing from 0.1 to 0.3 wt.%, and then shows slight decrement until 0.7 wt.%. An optimal combination of the tensile strength (193 MPa) and the elongation (17.8%) of as-cast A356 alloy was achieved with 0.3 wt.% of refining master alloy. Compared to the non-modified A356 alloy, the tensile strength and the elongation were improved by 10% and 242%, respectively.

Effects of Different Species of Sr Additives on as Cast Microstructure and Tensile Properties of AS31 Alloy

Effects of different species of Sr additives (pure Sr, cast Mg-10Sr block, Ф10mm extruded Al-10Sr bar) on as-cast microstructure and tensile properties both at ambient temperature and elevated temperature of AS31 alloy were studied. The experimental results showed that pure Sr, Mg-10Sr, Al-10Sr additions all could refine the grains of AS31 alloy obviously, modify the eutectic Mg2Si particles and strengthen AS31 alloy. Al-10Sr is most effective to refine microstructure and improve mechanical properties of AS31 alloy.

Effects of Different Sr Additions on As Cast Microstructure and Tensile Properties of AS31 Alloy

Effects of different Sr additions (0.1%-1%Sr, mass fraction) on as-cast microstructure and tensile properties both at ambient temperature and elevated temperature of AS31 magnesium alloy were studied. The experimental results show that the addition of Sr could refine the grain size obviously and modify the eutectic Mg2Si from Chinese script shape to polyhedral shape or fine fibers shape. The addition of Sr to AS31 alloy improved the tensile strength at ambient temperature, and the ultimate strength at 150°C first decrease and then increase with the Sr addition increase from 0.1% to 1%Sr.

Generating 2D Non-Equiaxed Initial Microstructure for Monte Carlo Simulation Using Modified Voronoi Model

A modified Voronoi model is established based on the Richards method to generate 2D non-equiaxed initial microstructure for Monte Carlo simulation. Microstructures produced by the ordinary Voronoi model are isotropic and cannot reflect the effects of the deformed grain shape on the annealing process. The modified Voronoi model based on ellipse set can be used to construct the deformed microstructure. The initial microstructure reflects the mean strain and the grain size distribution follows lognormal distribution.

Research of Short-Flow-Route Processes for Magnesium Alloys Prepared by Crystalline Magnesium

Long route and high inclusion content are two common problems existing in the present process for magnesium alloys. To solve these problems, a new process technology, in which the crystalline magnesium is used as the raw material, is developed. The process is melting flux→ adding raw materials in batches → stirring→ holding→ pouring (MASHP). The mechanisms of protection and purification mechanisms are also analyzed. The results show that the MASHP process has high protection and purification effects on magnesium alloys. By the in-batches addition mode of raw materials, no oxidation and evaporation loss of magnesium produce during heating and melting, and the inclusions that self-contained in the crystalline magnesium and that produced by oxidation during heating and melting can be minimized. High quality magnesium alloys can be produced by the new process.