Growth Feature of Crystals in Aluminum and Aluminum Alloy Welded with Laser

We investigate the development and the growth feature of columnar crystals in weld metals near the fusion boundary in 99.99% Al, A1050 and A5052 welded using laser. In the case of 99.99% Al, the columnar crystals which are developed epitaxially grow toward the center of the weld metals when shielded in argon. However, stray crystals are often observed in the weld metals shielded in nitrogen gas. This results from the development of cell structure and the competitive growth tends to occur due to the absorption of the trace of nitrogen gas in Al. The weld metals shielded in nitrogen gas are harder than the weld metals shielded in argon. This is caused by the development of AIN. The development of the strayy crystals becomes easier in A5052 than in A1050. In the case of A5052, it is very rare that epitaxial growth is clearly recognized and many stray crystals begin to grow from very near the fusion boundary. The growth rate of the columnar crystals increases as welding speed increases. The growth rate of columnar crystals when welded with pulse laser is faster than that welded with continuous laser. The maximum value obtained is 1.9 m/min and this is faster than that obtained in the weld metal welded by GTA.