Role of zinc coat in friction stir lap welding Al and zinc coated steel

Abstract

AC4C cast Al alloy and Zn coated steel were successfully lap welded using friction stir welding technology. Full strength joints could be obtained and the joints fractured at Zn coated steel base metal side, while Al alloy and unzinced steel could not be welded in the same welding conditions. The joining mechanism and the role of Zn coat on friction stir lap welding of Al alloy and Zn coated steel were put forward. The intervention of Zn coat promoted the formation of Al-Zn low melting point eutectic structure at the interface, which significantly improved the weldability of Al and steel.

Microstructure and Mechanical Properties of Al/Steel Friction Stir Lap Weld

“…Researchers have also studied Al/steel friction stir lap welding (FSLW) joint [18][19][20][21][22]. Kimapong and Watanabe [18] carried out that the maximum shear load of FSLW joint of 5083 aluminum alloy and SS400 mild steel could reach about 77% of aluminum alloy base metal.…”

“…Similar results were suggested by Lee et al [20] and they reported that 2 µm IMC layers with the composition of Fe 3 Al, Fe 4 Al 13 could contribute to the joint strength. Chen et al [21] used Zn coating on the steel surface to improve the weldability of Al and steel by means of promoting the formation of Al-Zn low melting point eutectic structure. Chen et al [22] also found that the thickness of IMC layer increased from 7.7 to 58.1 µm with decreasing welding speed, which significantly affected the joint strength.…”

Microstructural evolution during friction stir welding of dissimilar aluminum alloy to advanced high-strength steel

“…FeAl, FeAl 3 , and Fe 2 Al 5 were found in the interface under different tool tilt angle conditions. Chen et al [17] suggested the Zn coating on steel could improve the weldability of Al and steel through promoting the formation of Al-Zn low melting point eutectic structure. They also did another FSW lap joining study [18] and reported that the thickness of the IMC layer increases from 7.7 to 58.1 μm with decreasing welding speed, which significantly influences joint strength.…”

Friction Stir Brazing: a Novel Process for Fabricating Al/Steel Layered Composite and for Dissimilar Joining of Al to Steel

“…[8] On the other hand, friction stir lap welding (FSLW) of Al sheet to steel sheet has also been attempted in recent years, because a joint is produced in solid state and no cover gas or flux is used. [12] In the case of joining Al to galvanized steel, strong joining could be readily achieved, [13][14][15][16] because the presence of Zn coating can produce the formation of a soft zone [13] or Al-Zn eutectic [14,15] at the bond interface, which contributes to the intimate contact or effectual mutual diffusion between the base metals. However, in most cases of joining Al to non-galvanized steel, there are some problems as follows.…”