A sessile drop method was applied to study the wetting and spreading behavior of pure aluminum (99.99%) and commercial aluminum alloy 226D (10.75 Si, 3.3 Cu, 0.75 Fe, 0.2 Mg, 0.215 Mn, 0.135 Ti, wt.%) on the Ni-P coatings containing 2-8% P and deposited by electroless method on Ni substrates.
The tests were performed under vacuum at a temperature of 700°C for different times of contact using non-contact heating to the testing temperature coupled with capillary purification by squeezing a liquid droplet from graphite capillary at the testing temperature, directly during wettability tests under vacuum conditions. Comparative measurements were also done on uncoated Ni substrates. Wetting and spreading behavior was recorded using high-speed CCD camera.
The detailed structural characterization of interfaces in the solidified sessile drop samples were made by light microscopy and scanning electron microscopy coupled with EDS analysis.
The results obtained are discussed from point of view of the role of phosphorus content in Ni and alloying additions to Al on the interrelationship between wetting and spreading behavior and the formation of interfacial reaction products and mass transfer through the drop/substrate interface.