TECHNICAL ARTICLE Effect of Al Addition on Electrochemical Behavior of Sn-0.7Cu-xAl Lead-Free Solders Alloys in 3.5 wt.% NaCl Solution Dheeraj Jaiswal , Dileep Pathote, Vikrant Singh, and C.K. Behera Submitted: 9 December 2021 / Revised: 19 January 2022 / Accepted: 30 January 2022 The corrosion behavior of alloys is highly significant as far as lead-free solder applications are concerned. The corrosion performance of the alloy is dependent mainly on the composition of the alloys. In this investigation, the effect of Al adding on the electrochemical behavior of Sn0.7Cu-xAl (x = 0, 1, 2 and 3 wt. percent) lead-free solders has been investigated using electrochemical techniques in neutral 3.5 wt.% NaCl solution at ambient temperature. The influence of aluminum additions on the microstructure of Sn-0.7Cu- xAl lead-free solder alloys was also examined. The microstructure shows that the b-Sn, eutectic and intermetallic compound (IMC) are present in the Sn-Cu-Al solder alloys. At the same time, the addition of aluminum refined the microstructure of the Sn-0.7Cu alloys. Cu 6 Sn 5 is the interfacial IMC at the b-Sn border in the Sn-0.7Cu-xAl, while Al 2 Cu is the interfacial IMC in the Sn-0.7Cu-xAl. Electrochemical impedance spectroscopy (EIS) results indicate that the corrosion product layer was affected by Al addition, which changed the electrochemical corrosion behavior from charge transfer to diffusion control. By adding just 1 wt.% of Al to Sn-0.7Cu solder, the microstructure was refined, and corrosion resistance was im- proved, as shown by decreased corrosion current density (I corr ) and increased total resistance (R t ). Excess Al addition (above 1 wt.%) led to Al-containing IMCs, which were verified as Al 2 Cu, worsening the corrosion resistance of Sn-0.7Cu-xAl solders. The primary corrosion products were verified as Sn 21 Cl 16 (OH) 14 O 6 combined with a small quantity of oxide/chloride of Sn compounds. Keywords Corrosion, EIS analysis, Lead-free Solder alloys, Potentiodyanmic Polarization 1. Introduction Solder alloys have been commonly used to join electrical components in the electronic industry. It provides good electrical interconnection and mechanical support. Lead-based solder alloys such as eutectic and near eutectic of Sn-37Pb have been dominating in the field of soldering for the last many decades due to their various attractive mechanical and physical properties, reliability, reflowing temperature (183 °C), good wettability, low cost and mechanical properties. There are two main issues with lead-based solders toxicity and environmental concern. As a result, the new lead-free solder alloys develop- ment is the only alternative in this field of research (Ref 1). After lots of effort put by many researchers to develop lead- free solder alloys to replace conventional lead-based solder alloys, it is resulting in several possible alternatives, including Sn-Cu, Sn-Zn, Sn-Ag, Sn-Cr, Sn-In and Sn-Al solder have been established to date (Ref 2-10). Sn-Cu alloys have been regarded as an excellent replacement for lead-containing solder alloys among the different alternative lead-free solder alloy systems because of their low impurity sensitivity and good performance, low cost and low-melting temperature (227 °C) (Ref 11-13). However, the main drawback of this alloy is that the presence of coarse precipitate of Cu 6 Sn 5 phase improves the pitting sensitivity and reduce its corrosion resistance. Thus, the corrosion properties can be enhanced by refining the Cu 6 Sn 5 phase without compromising other properties. Method of alloying can be an effective way to refine the microstructure of solder alloys. Several alloys of material such as Fe, Zn, Sb, Bi, Ce, Ni and Co (Ref 14, 15) have been alloyed to binary Sn- Cu solder alloys to improve mechanical and wettability properties and refine microstructure (Ref 16). The addition of In and Ag to the Sn-0.7Cu alloy enhances the tensile and creeps properties due to dispersion strengthening and grain refining of SnIn 4 and Ag 3 Sn compound (IMCs) Cu 6 Sn 5 , and Cu 3 Sn IMC formation was halted by AlCu (IMCs) created in the bulk of the solder, which then migrated to the solder/Cu interface and eventually replaced the previously formed IMCs until finally converting to Al 2 Cu 3 (IMCs) dispersed back into the bulk of the solder. The Sn-9Zn eutectic solder alloy has a microstructure refined with Cu and Al, and the Eutectic solder alloy is made uniform with IMC’s (Al 6 Zn 3 Sn and Cu 5 Zn 8 ). With the second step of dispersal enhancement, the tensile strength of the alloys is increased by the intermetallic compound Al 6 Zn 3 Sn (IMC) (Ref 17). In contrast, the tensile strength of the solder alloys is lowered by the presence of a significant Cu 6 Sn 5 shaped flower and a Cu 5 Zn 8 installed rock that weakens the cross-sided b-Sn matrix. Dheeraj Jaiswal, Dileep Pathote, Vikrant Singh, and C.K. Behera, Department of Metallurgical Engineering, IIT(BHU), Varanasi 221005, India. Contact e-mail: dheerajjaiswal.rs.met17@itbhu.ac.in. JMEPEG ÓASM International https://doi.org/10.1007/s11665-022-06771-y 1059-9495/$19.00 Journal of Materials Engineering and Performance