TIN-BASED LEAD-FREE SOLDERING ALLOY WITH IMPROVED PROPERTIES AND PROCESS FOR PREPARING THE SAME

摘要

The invention relates to a tin-based lead-free soldering alloy also containing other alloying elements such as Ag, Cu, Mn, Ti or rare earths in various ratios, the alloy being used for joining components of Cu or other Cu alloys in the electrotechnic and electronic field and to a process for preparing the same. The claimed alloy has the following chemical composition: 95...97.5% Sn, 2.8...3.8% Ag, 0.5...0.9% Cu, max. 0.05% Mg, max. 0.05% Ti and max. 0.05% rare earths, the percentage being expressed by weight. The claimed process consists in dosing the metal elements such as Sn, Ag, and Cu with a purity of minimum 99.5%, fusing the same in a resistor electrical furnace up to a temperature ranging between 450...550°C when there is carried out the microalloying with Mn, Ti and rare earths under an amount of 0.5...1% of protection and refining flux layer comprising 82% SnCland 18% ZnCl, lowering the temperature of the melt down to 300...350°C when the casting in metal moulds or core moulds is carried out to obtain cylindrical rods which are processed by cold extrusion with a specific force of 30...35kN/cm, and then cold drawing in steps with a reduction of 3...10% with intermediate annealings at 125...150°C there finally resulting wires with diameters ranging between 1.5...2 mm having the ultimate tensile strength of 32...45N/mm, the yield point of 28...35N/mm, the elongation on break of 15...25% and hardness of 15...18HV, the melting temperature ranging between 217...222°C, specific conductivity of 13.5...14.5% IACS, good flowing characteristics in liquid state with the soldering joint of 0.1...0.5 mm and wetting angle on copper support of 10...12°.