STUDY INTO STRUCTURE AND PROPERTIES OF SOLDERS BASED ON ALUMINUM AND ZINC IN THE FORM OF SMALL-SECTION CAST BARS

The study covers Al–Cu–Si (A34 grade) and Zn–Al–Cu (Welco52 grade) solders. It is found that A34 solder (Al–28%Cu–6%Si) melts and crystallizes in a narrow range of temperatures (~18 °C). Solidus and liquidus temperatures of A34 solder are ~508 °С and ~526 °С, respectively. Zn–Al–Cu (Zn–4%Al–2,5% Cu) solder has a eutectic composition, so it melts and crystallizes at a constant temperature of ~389 °С. Densities of investigated solders in their liquid and solid states are studied. A34 solder has a density of 3,02 and 3,32 g/cm3 , respectively. Zinc solder density is 6,28 g/cm3 in the liquid state, and 6,69 g/cm3 in the solid state. The influence of casting conditions on the structure of cast alloys in the form of bars with cross sections of 13, 10, and 5 mm2 was investigated. Main structural components of solder alloys reduce in size as cross sections decrease. The aluminium-based solid solution dendrites and CuAl2 phase are reduced in the A34 solder microstructure. In zinc solders, the most severely reduced ones are zinc-based solid solution dendrites. The best castability is observed in melts obtained from 5 mm2 section bar solders with studied sample gaps of 2,0, 1,5 and 1,0 mm. Eutectic zinc solder features better castability in comparison with A34: castability of the melt obtained from the 5 mm2 section zinc solder rod with a sample gap width of 2,0 mm is 100 % (for A34 melt solder obtained from a rod of the same cross section it was 98 %). Experiments on soldering AK12 alloy plates and 3003 alloy sheets demonstrated that there is a tight border in the solder/base material system and no any defects such as pores or unsoldered areas. There was a slight interpenetration of solder alloys into base materials, especially when soldering AK12 cast plates.