| Magnesium alloys and steels are widely used in daily life and industrial production,such as aerospace,automotive,military and electronics.With the development of science and technology,the trenchant requirements of material performance cannot meet by a single type of material.Magnesium alloys and steels have their own advantages in performance.Magnesium alloys are the lightest engineering metal materials with high specific strength,specific stiffness,good electromagnetic shielding ability and absorption capacity for oscillating noise.And,steel is the most widely used metal structural material in modern industry and has good mechanical properties.If a magnesium alloy is combined with steel to prepare a Magnesium/Steel bimetal composite material,the excellent properties of the two materials can be combined to achieve an improvement in comprehensive performance,which will expand the range of applications for both metals.Because of magnesium alloy and the steel have a large distinction in melting point,also magnesium alloy with low boiling point,it is difficult to through fusion to achieve the connection,even Fe and Mg in molten state at the same time also extremely difficult to miscibility,and no interactions between them,not directly mesophase formation.It is a challenge to compound magnesium alloy with steel.It is often necessary to introduce interlayer metal between the two to realize the metallurgical combination of the two metals.At present,the commonly used welding way to realize the Mg/Steel bimetal composite,the liquid-solid compound casting technology,this paper first on hot dip aluminized Steel surface to form a layer of the middle layer,and then pouring liquid molten magnesium alloy,magnesium alloy and Steel was successfully metallurgy composite,mainly studies the hot-dip temperature,immersion plating time,pouring temperature and liquid-solid product than liquid-solid casting compound Mg/Steel bimetallic interface,analyzes the Mg/Steel bimetal organization performance characteristics.The main work of this paper is as follows:The effect of different dip temperature and dip time on the bonding effect of aluminum alloy coating with steel was studied.With the decrease of dip-plating temperature or dip-plating time,the metallurgical bonding layer cannot be formed on the surface of the steel.Increasing the dipping temperature or prolonging the dip time will increase the thickness of the interface reaction layer.However,when the dip plating temperature is too high or the dip plating time is too long,it will lead to the serious deformation of the steel tube and the reduction of the wall thickness.When the immersion temperature is 770 ° C and the immersion time is 10 min,a uniform and dense interfacial reaction layer can be obtained.The entire interface reaction layer can be divided into three layers.From the iron matrix to the aluminum matrix,the Fe2Al5+?10-Al9Fe4Si3 phase,the FeAl3 phase,and ?6-Al4.5FeSi phase are obtained,respectively,and the interface reaction layer surface smearing a dense layer of aluminum alloy,scratches the experimental results show that aluminum alloy coating and steel combination effect is good.Based on the above research,Mg/Steel bimetallic castings were successfully prepared by the liquid-solid composite casting by introducing al-si alloy as the intermediate layer through the hot-dip aluminum plating process.The effects of casting temperature and liquidsolid product ratio on microstructure and properties of Mg/Steel bimetallic interface were studied.The results show that the phase composition of the Mg/Steel bimetallic interface is approximately the same under different pouring temperatures and liquid-solid product ratios.Pouring temperature of liquid-solid composite casting Mg/Steel bimetallic interface has a great influence on the quality,pouring temperature of 720 ? and 750 ?,the magnesium substrate near the interface reaction layer there is obvious gap,cause fracture in aperture place bimetal,lead to Mg/Steel bimetal shear strength is relatively low;When pouring temperature is 780 ?,Mg/Steel bimetal relatively compact as a whole.In addition,the liquid-solid ratio also had a great influence on the interface quality of Mg/Steel bimetal.As the liquid-solid ratio decreased,the thickness of the reaction layer at the Mg/Steel bimetal interface increased,and the magnesium matrix near the reaction layer showed gap defects and its width increased.When pouring temperature is 780 ?,liquid-solid volume ratio is 12,Mg/Steel bimetallic interface quality is good,high shear strength,reached 23.3 MPa,double metal fracture appears as brittle fracture,mainly occurs at the interface layer between Al12Mg17 and FeAl3.The combination of the hot-dip aluminized Magnesium/Steel bimetallic interface and the un-aluminized interface was compared under the same casting temperature and liquidsolid ratio parameters.There is no element diffusion at the interface of the un-aluminized Magnesium/Steel bimetal.And,there is a gap between the two sides of the matrix,the void ratio is relatively higher,and the shear strength rather poor,being 2.43Mpa;and the hot-dip aluminized Magnesium/Steel bimetal has an interfacial reaction layer,the two matrices are tightly bonded.And the void ratio at the interface is relatively lower,and the shear strength is 8.59 times higher than that of the control group.In addition,the hardness results at the hotdip aluminized Mg/Steel bimetallic interface show that the hardness of the interface reaction layer is between 10-13 gpa,much higher than the hardness of the matrix on both sides.In this paper,hot dip aluminum plating and liquid-solid composite casting method were used to solve the problem of magnesium alloy and Steel metallurgical composite,and Mg/Steel bimetallic castings with good metallurgical interface and mechanical properties were obtained,which provided theoretical basis and technical support for the preparation and forming of Mg/Steel bimetallic materials. |
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