Interfacial Reactions of Zn-Al Alloys with Na Addition on Cu Substrate During Spreading Test and After Aging Treatments

Spreading tests for Cu substrate with Zn-Al eutectic-based alloys with 0.2, 0.5, and 1.0 wt.% of Na were studied using the sessile drop method in the presence of QJ201 flux. Spreading tests were performed for 1, 3, 8, 15, 30, and 60 min of contact, at the temperatures of 475, 500, 525, and 550 A degrees C. After cleaning the flux residue from solidified samples, the spreading area of Zn-Al + Na on Cu was determined in accordance with ISO 9455-10:2013-03. Selected, solidified solder-substrate couples were cross-sectioned and subjected to scanning electron microscopy of the interfacial microstructure. The experiment was designed to demonstrate the effect of Na addition on the kinetics of formation and growth of CuZn, Cu5Zn8, and CuZn4 phases, which were identified using x-ray diffraction and energy-dispersive spectroscopy analysis. The addition of Na to eutectic Zn-Al caused the spreading area to decrease and the thickness of intermetallic compound layers at the interface to reduce. Samples after the spreading test at 500 A degrees C for 1 min were subjected to aging for 1, 10, and 30 days at 120,170, and 250 A degrees C. The greater thicknesses of IMC layers were obtained for a temperature of 250 A degrees C. With increasing Na content in Zn-Al + Na alloys, the thickness reduced, which correlates to the highest value of activation energy for Zn-Al with 1% Na.