| Sn-Bi alloy is a kind of low melting point and environmentally friendly alloy.With the melting point in the range of 139℃ to 232℃, It’s the most close to the raditional Sn-Pb alloy. Due to the low melting point, good wettability, abundant mineral resources, etc, it have been widely used as low temperature brazing material, temperature sensitive components, fuse and lightning protection element. However, as the hard brittleness microstructure of Bi in the alloy, it is restricted in production and application, especially, as a fuse or electronic components of small diameter wire, the small diameter wire material is easy to break during the preparation process, and the yield is low.According to these questions which the present situation of the production and application limitation of poor plasticity of Sn-Bi small diameter wire. A proposal for the preparation of Sn-52Bi alloy wire with good plasticity which is by semi-solid stirring processing and porous extrusion technique was proposed, in the article. The preparation processing of preparing small diameter wire is studied by DEFORM software and extrusion test. The evolution and mechanism of microstructure and properties of semi-solid Sn-52Bi alloy in plastic extrusion is explored by metallographic microscope, universal strength testing machine, SEM (scanningelectron microscope) and electrochemical work station test equipment. The purpose of the study is to provide experimental and theoretical reference for the preparation of high performance lead-free Sn-Bi alloy and its application in the electronics industry.Research shows that the microstructure of Sn-52Bi is composed of the primary phase β-Sn and the eutectic composition. The β-Sn is changed from dendritic to near spherical or spherical and the plasticity has been improved after adding mechanical agitation or ultrasonic stirring to Sn-52Bi alloy slurry, in semi-solid interval. In ultrasonic agitation process, The elongation of semi-solid alloy prepared by ultrasonic stirring 2min at 140 is 42.75%. Compared with the process of water cooling at 180℃(Ordinary water cooling process), it increased by 137.1%. After the tensile test, the fracture morphology of the alloy was analyzed. shows a feature of ductile fracture, the dimple and small cleavage step are doped with each other in fracture morphology. Corrosion resistance analysis showed that the corrosion resistance of bar alloy was improved by semi-solid stirring, and the self-corrosion current density of the bar alloy which prepared by ultrasonic stirring 2min at 145℃ was 17.7231 μ A·cm-2. Compared with the sample which prepared by ordinary water cooling process, the self-corrosion current density is reduced by 74.1%.Die angle is set to 30°, calibrating strap length is set to 5 mm, die hole distance is set to 1.5 mm and the material strength of the mold should be greater than 1000MPa after the semi-solid Sn-52Bi alloy extrusion die is optimized by DEFORM finite element software. Wire extrusion process is analyzed after mold is processed, The results show that the plasticity of the alloy bar is poor, the extrusion force is increased, and the maximum extrusion pressure is in the range of 30-40kN, it is in agreement with the result of simulation. Sn-52Bi alloy extrusion simulation is found that the size and distribution of stress are relatively uniform, the maximum equivalent stress is about 270MPa, the strain of die chamfering edge position is slightly larger than the center’s, in the process of extrusion of Sn-52Bi alloy bar.The micro structure and mechanical properties of Sn-52Bi alloy after extrusion shows that Bi-phase can not be completely broken during the extrusion and the heart is still with the mesh connected, due to micro structure of Sn-52Bi prepared by ordinary water cooling process is mesh structure, But in the microstructure of Sn-52Bi that prepared by Semi-solid stirring, the Bi-phase is broken into discrete wormlike and the microstructure is uniform, the difference of stress and strain distribution is not obvious to the uniformity of the wire. Corrosion resistance analysis showed that the corrosion resistance of wire alloy was improved with semi-solid stirring, and the corrosion resistance of the wire is worse than that of the bar, but the change is the same as that of the bar and the best of corrosion resistance of wire and bar is the sample prepared with ultrasonic stirring 2min at 145℃, the self-etching current density is 28.7734 u A·cm-2. After extrusion, the plasticity of the wire material has been greatly improved, compared with the bar sample, the elongation rate is increased by more than 300%. Fracture morphology is also the same as the bar, but the cleavage step of Bi is smaller. |
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