Preparation Of Semi-Solid Sn-52Bi Alloy And Material Properties

Sn-Bi alloy is a kind of lead-free low melting point alloythat applied in 100～200℃, whichis suitable for solder and thermal fuse and other electronic components. But the traditional casting and extrusion method of alloy brittleness is big, thus made it difficult to meet the requirements. As the awareness of traditional solder harmful to the environment, lead-free solder is gradually replacing of the lead solder, scholarshave researchedmuch about the lead-free solder with aSn-Bi alloy home and abroad, but the research of low melting point (100℃-200℃) lead-free fusible alloy about using in electrical appliances, fire control and alarm device are is less.Due to this situation, this article is based on the hypoeutectic Sn-52Bi alloy as the main research object. This topic adopteda method of mechanical agitation, ultrasonic vibration method and compound mixing to prepare Semi-Solid Sn-52Bi alloy specimens. The OM, SEM, XRD, DSC-TG, Universal mechanical testing machine, Neutral salt spray corrosion test chamber, Electrochemical workstation and so on were used to test the metallographic structure, surface appearance,phasecomposition, ductility, latent heat fusion, and anti-corrosion and so on, The effect of non-dendrite semi-solid organization onthe plastic alloy, the latent heat of fusion and corrosion resistance wasexplored. In order to optimize the preparation of the high plasticity of Sn-52Bi alloy to provide technology and theory basis, the effect of composite mechanical stirring and ultrasonic stirring on semi-solid alloy organization was studied.Research shows that:In a certain range of the stirring time, stirring temperature and stirring rate, Semi-solid forming of mechanical stirring or ultrasonic vibration or combination stirring refining primary grain is discussed.Primary phaseβ-Snchanged dendrite into globular, X-ray diffractometer results reveal that the lattice parameters, chemical constitution of the nano-particles are the same as raw material and no new phase appears.When using mechanical stirring for 5 minutes then ultrasonic and mechanical stirring 2 minute in 150℃ alloy specimen has the highest elongation and the minimum,latent heat of fusion, They are respectively49.13% and 49.51 J/g. Compared with the common casting, semi-solid alloysthe elongation of semi-solid alloy increased by 170.2%.According to the international standard of metal corrosion, set static immersion corrosion and neutral salt spray accelerated test and electrochemical corrosion experiment method, studied and analyzed the corrosion resistance of Sn-52Bialloy both semi-solid casting and common casting. Using the weight loss test to measure the corrosion rate of the alloy in the immersion corrosion, the corrosion surface appearance of alloy was researched by scanning electron microscopy (SEM) after immersion corrosion and neutral salt spray accelerated test.Use anode polarization curve and ac impedance to analysis the corrosion potential, corrosion current, ac impedance values and capacitive reactance radius size. Research shows that:thecorrosion rate of common casting is 10-7. Semi-solid casting is 10-8.Cl- penetrated into the alloy from grain boundary. The corrosion rate of semi-solid alloy, the width and depth of the grain boundary corrosion are lower than the common casting alloy. The corrosion resistance of globular β-Sn semi-solid alloy improved.