Chromium effects on the microstructural, mechanical and thermal properties of a rapidly solidified eutectic Sn-Ag alloy

摘要

Purpose - This study aims to investigate the chromium (Cr) effects on the microstructural, mechanical and thermal properties of melt-spun Sn-3.5Ag alloy. Design/methodology/approach - Ternary melt-spun Sn-Ag-Cr alloys were investigated using X-ray diffractions, scanning electron microscope, dynamic resonance technique, instron machine, Vickers hardness tester and differential scanning calorimetry. Findings - The results revealed that the Ag_3Sn intermetallic compound (IMC) and β-Sn have been refined because of the hard inclusions' (Cr atoms) effects, causing lattice distortion increasing these alloys. The tensile results of Sn_(96.4)-Ag_(3.5)-Cr_(0.1) alloy showed an improvement in Young's modulus more than 100 per cent (42.16 GPa), ultimate tensile strength (UTS) by 9.4 per cent (23.9 MPa), compared with the eutectic Sn-Ag alloy due to the high concentration of Ag_3Sn and their uniform distribution. Shortage in the internal friction (Q~(-1)) of about 54 per cent (45.1) and increase in Vickers hardness of about 7.4 per cent (142.1 MPa) were also noted. Hexagonal Ag_3Sn formation led to low toughness values compared to the eutectic Sn-Ag alloy, which may have resulted from the mismatching among hexagonal Ag_3Sn phase with orthorhombic Ag_3Sn and β-Sn phases. Mechanically, the values of Young's modulus have been increased, with increasing chromium content, whereas the UTS and toughness values have been decreased. The opposite of this trend appeared in Sn_(95.8)-Ag_(3.5)-Cr_(0.7) alloy, which may have been due to high lattice distortion (ε=16.5×10~(-4)) compared to the other alloys. Increase in the melting temperature T_m, ΔH, C_p and ΔT was because of Ag_3Sn IMC formation. The low toughness of Sn_(96)-Ag_(3.5)-Cr_(0.5) and Sn_(95.8)-Ag_(3.5)-Cr_(0.7) (109.56 J/m~3 and 35.66 J/m~3), relatively high melting temperature Tm (223.22°C and 222.65°C) and low thermal conductivity and thermal diffusivity (32.651 w.m~(-1).k~(-1) and 0.314 m~2/s) make them undesirable in the soldering process. The high UTS, high E, high thermal conductivity and diffusivity, low creep rate and low electrical resistivity, which have occurred with "0.1 Wt.%" of Cr, make this alloy desirable and reliable for soldering applications and electronic assembly. Originality/value - This study provides chromium effects on the structure of the eutectic Sn-Ag rapidly solidified by melt-spinning technique. In this paper, the authors compared the elastic modulus of the melt-spun compositions, which have been resulted from the Static method with that have been resulted from the Dynamic method. This paper presents new improvements in mechanical and thermal performance.