Study On Refinement Effect And Refinement Mechanism Of K₂TiF₆ On Magnesium And AZ61 Alloys

As the times progress,energy saving and emission reduction has become extremely important.Magnesium and its alloys have attracted more and more attention as the lightest common metal structural materials.However,due to the low strength,poor creep resistance,poor plasticity and corrosion resistance of magnesium alloys,it has also restricted the development of magnesium alloys.Therefore,how to improve the mechanical properties of magnesium alloys has become a hot spot in the research of magnesium alloys.According to the Hall-Petch formula,the yield strength of the alloy is inversely proportional to the square root of the grain size.Studies have shown that as the grain size is refined,not only the strength of the material is greatly improved,but also the plasticity is significantly improved.Ti element is similar to Zr element and has extremely strong grain refining effect.Ti element can be applied to a wider range of Al-containing magnesium alloys.Therefore,this paper summarizes and analyzes the research status of microstructure and properties of Ti element refined magnesium alloy at home and abroad.On the basis of this,a method of introducing Ti element by adding titanium salt?K₂TiF₆?was designed to improve the microstructure and mechanical properties of magnesium alloy.The paper is divided into two parts:1.Taking pure magnesium as the research object.The effect of K₂TiF₆ on its grain size and microstructure was studied by conventional casting method.The study found that after adding K₂TiF₆ to pure magnesium,the grain size gradually became smaller as the amount of addition increased.When 1.5wt.%Ti,the refining effect is the best,the columnar crystals completely disappear,the equiaxed crystals are fine and evenly distributed,and the refining effect can reach 89%compared with the pure magnesium which is not refined.Microstructure analysis showed that the Ti element formed by the reaction did not segregate or form a new phase in the?-Mg matrix,but was evenly distributed in the Mg matrix.This distribution form a key role for pure magnesium refinement.Different reaction temperature experiments were carried out on the optimal refining effect.It was found that K₂TiF₆ not only promoted the formation of equiaxed crystals of pure magnesium,but also significantly reduced the grain size as the reaction temperature increased.2.Taking AZ61 alloy as the research object,the effect of K₂TiF₆ addition on its grain size and microstructure was studied,and its solution and aging treatment were carried out.The mechanical properties were measured.It was found that K₂TiF₆ was added to AZ61 alloy.With the addition of K₂TiF₆,the grain size gradually decreased.When the pre-furnace 1.5 wt.%Ti was reached,the refining effect was the most obvious,which was nearly 76%thinner than the original AZ61 alloy.Different from pure magnesium,the addition of K₂TiF₆ will coarsen the crystal grains as the reaction temperature decreases.This is because the low reaction temperature does not fully react K₂TiF₆ with Mg to form a small amount of Ti,and the Ti element and AZ61 alloy.The Fe element forms a compound,which reduces the heterogeneous core of AZ61and coarsens the crystal grains.Microstructure analysis of 1.5 wt.%Ti in front of the furnace showed that Ti element was evenly distributed on the second phase and the matrix,which not only inhibited the growth of the grains,but also refined the second phase,gradually from the original coarse network structure.It becomes smaller and more evenly distributed.After solid solution+aging treatment,the tensile strength,elongation and yield strength of the samples were improved compared with the as-cast condition.The tensile strength and elongation of the AZ61 alloy of 1.5 wt.%Ti before the furnace reached 201.5 MPa and 11.5%.