Effects Of Micro Ti On Microstructure And Properties Of Mg-based Amorphous Alloy

Mg-based amorphous alloys?Bulk Metal Glass?have become recognized as new green structural materials due to the advantage of wide sources,low cost,high strength,high specific strength,corrosion resistance and other properties.However,the low plasticity of Mg-based amorphous alloy seriously affects the engineering application.In order to solve it,Mg-based amorphous alloys with high-strength and high-ductility was prepared by an elemental substitution method.At the same time,the preparation of amorphous alloys has the disadvantages of high cost,low efficiency and unability to be continuously produced,which greatly impede the development and application of amorphous alloys.The Ohno Continuous Casting?OCC?process can improve the efficiency of the preparation of amorphous alloys.And this method have great significance for the development of magnesium-based amorphous alloys.In this paper,Mg_58.5Cu_30.5Y₁₁ with high glass forming ability?GFA?was selected from the Mg-Cu-Y system,in which titanium?Ti?was added with addition of 5 at.%,8 at.%,and12 at.%.The electronegativity difference?x the difference in atomic size?,???·?x?and?.??/?x?were calculated for the system of the(Mg_58.5Cu_30.5Y₁₁)_100-xTi_x?x=0,5,8 and 12?alloy.These results showed that the feasibility of forming an amorphous alloy is proper after the incorporation of Ti element according to the theoritical calculation.The Mg_58.5Cu_30.5Y₁₁1 amorphous alloy was prepared by a copper mold method.When the pouring temperature was increased from 550 K to 650 K,the change tendency of the number of crystalline component was"concave".It was found that at the melt temperature of 600 K.The best fluidity and superheat reached the maximum benefit,and casting products were fully amorphous.(Mg_58.5Cu_30.5Y₁₁)_100-xTi_x?x is a content of Ti?amorphous alloys were prepared with Mg_58.5Cu_30.5Y₁₁ as the matrix.When the Ti content was increased from 0 at.%to 12 at.%:the crystallization temperature of T_x for the alloy decreases gradually with the increase of Ti content.The value of?T_x in the supercooled liquid region exhibited a decreasing trend.And the amount of doped Ti was inversely proportional to the glass forming ability of(Mg_58.5Cu_30.5Y₁₁)_100-xTi_x.The(Mg_58.5Cu_30.5Y₁₁)_100-xTi_x?x content of 0 at%,5 at%,8 at%and 12 at%?alloys had a yielding phenomenon before fracture during compression,and their fracture strengths of679.211 MPa and 768.328 MPa,905.342 MPa and 794.442 MPa respectively.Compared with that of the matrix,the fracture strength of the doped alloy was increased about 13.1%,33.3%and 17.0%,respectively.The structure of the sample was characterized by scanning electron microscopy?SEM?and differential scanning calorimetry?DSC?.It was found that the(Mg_58.5Cu_30.5Y₁₁)₉₂Ti₈ sample with Ti=8 at.%had the best performance prepared by the copper mold casting method.Its thermodynamic parameters T_x?crystallization temperature?,T_g?glass transition temperature?,and?T_x?supercooled liquid phase region?were 474 K,426 K,and 48 K,respectively.The effect of OCC process parameters on the GFA of Mg_58.5Cu_30.5Y₁₁ amorphous alloy was investigated.First,the process parameter was the temperature of the mold mouth.According to the surface quality and the XRD diffraction pattern,the profile temperature of the amorphous alloy was selected was 800 K.Secondly,for the temperature parameters as the quantitative analysis,the samples'casting speedes are 12 mm/min,18 mm/min and24 mm/min respectively.When the speed of casting is 18 mm/min,the surface quality is smooth,and the length of the sample is 14.8 cm.Further,the effect of cooling distance on Mg-based amorphous alloy was investigated.The analysis of microstructure and hardness test were carried out for the samples of the process parameters of 60 mm and 75 mm,respectively.The results showed that Mg-based amorphous composites with the length up to 17.7 cm is fully amorphous,which was continuously produced at a melt temperature of735 K with a holding time of 1 h,a mold mouth temperature of 800 K,a casting speed of18 mm/min and a cooling distance of 75 mm.Our investigation proved that it is feasible to prepare Mg-based amorphous alloy by using the OCC process.