Effects of aging on microstructure evolution and mechanical properties of high-temperature Zn-4Al-3Mg solder

Abstract

Purpose

This paper aims to investigate the transformations during aging at 200°C for different periods on microstructure and mechanical properties of high-temperature Zn-4Al-3Mg solders.

Design/methodology/approach

The solder was melted in a resistance furnace, and different cooling rates were obtained by changing the cooling medium. Subsequently, all the specimens were aged at 200°C for 20 h and 50 h. A scanning electron microscope equipped with an energy dispersive X-ray detector and X-ray diffraction were used for the observation of microstructures and the determination of phase composition. Tensile tests and Rockwell hardness tests were also performed.

Findings

After aging, Zn atoms precipitated from the supersaturated α-Al and the (α-Al + η-Zn)_eutectoid phase with the original fine lamellar structure coarsened and spheroidized to minimize the system energy. Among these solders, the furnace-cooled alloys exhibited the highest thermal stability, largely retaining their original morphology after aging, whereas the collapse and spheroidization of the η-Zn phase and the coarsening of the η-Zn dendrites took place in the air-cooled and water-cooled samples, respectively. Furthermore, a decrease in tensile strength during aging was attributed to the thermal softening effect. The variation of macro-hardness was mainly associated with the microstructural alterations in terms of quantity, morphology and distribution of soft η-Zn phase and hard intermetallic compounds induced by the aging treatment.

Originality/value

The structural stability of eutectic Zn-4Al-3Mg solders solidified at different cooling rates and the effect of aging on mechanical properties were investigated.

Citation

Wang, H., Liu, Y., Gao, H. and Gao, Z. (2014), "Effects of aging on microstructure evolution and mechanical properties of high-temperature Zn-4Al-3Mg solder", Soldering & Surface Mount Technology, Vol. 26 No. 4, pp. 203-213. https://doi.org/10.1108/SSMT-10-2013-0025