The Preparation Of In-situ Graphene Inoculation And Its Effect On Grain Refinement Of Magnesium Alloys

Magnesium alloys are known as "the green engineering material of the 21 st century",which have very broad applications in the fields of automobiles,aerospace,electronics and so on.Grain refinement is of great significance to magnesium alloys.At present,Zr is the most successful commercial inoculation in non-Al Mg alloys,but it is not applicable to Mg-Al alloys,and carbon-containing inoculation is currently popular in Mg-Al alloys.This research is intended to develop a kind of low-cost,high-efficiency and universally applicable grain inoculation for magnesium alloys.Using pure magnesium and high-purity CO2,the graphene inoculation agent was successfully prepared by the in-situ reaction method,which greatly reduced the production cost of the graphene inoculation.The graphene inoculation agent has wrinkles and some defects,and adheres nano-magnesium oxide on its surface,containing about 3-15 layers of graphene units.Plastic deformation can effectively change its morphology.The graphene inoculation was used to refine the Mg alloys.The Mg alloys system is divided into Mg-Al and non-Al Mg alloys.The graphene inoculation has almost no refinement effect on pure Mg and negatively refinement effect on the Mg-3Y alloys.And it has a little refinement effect on the Mg-3Zn alloys,although the refinement effect of graphene inoculation is not as effective as the Zr inoculation,but it can improve the hotcracking tendency of the Mg-Zn alloys.The graphene inoculation has obvious refinement effect on Mg-Al binary alloys.After adding 10 wt.% of graphene inoculation,the refinement efficiency of Mg-0.5Al,Mg-1Al,Mg-3Al and Mg-9Al alloys reached 82.58%,83.64%,57.2% and 50.7% respectively.Identically,the graphene inoculation has efficiency refinement effect on commercial Al-containing magnesium alloys,which changes the morphology of as-cast grains and transforms dendrites into rose-like equiaxed grains.The mechanical properties of Mg-Al alloys are greatly improved by the graphene inoculation.When the graphene inoculation is used to refine the Mg-Al alloys with holding time at 20-40 min,the refinement effect is the best.The cooling rate has a positive effect on the refinement of the Mg-Al alloys.The faster the cooling rate,the finer the grain size,and the higher the refinement efficiency.The refinement effect by graphene inoculation on non-Al Mg alloys is mainly because of the obstacle of solute elements during solidification.Al4C3 particles are effective heterogeneous nucleations of ?-Mg,resulting in the effective refinement behavior on Mg-Al alloys.