Study on Microstructure and Properties of Laser Beam Welded 2060 Al-Li Alloys Filled with ER4047 Wire

Abstract:

The newly developed Al-Li alloy 2060 has broad application prospects in the field of aeronautics and astronautics with the characteristics of light weight and high strength. In this paper, 2060 Al-Li alloy was tested by means of laser beam welding filled with ER4047 welding wire. The morphology and microstructure of the weld, the micro segregation of the alloy elements, the precipitation of the second phases and the mechanical properties of the weld were studied by means of optical microscope, scanning electron microscope, electron probe micro analyzer(EPMA) and transmission electron microscopy(TEM), X-ray diffractometer (XRD), micro hardness test, tensile test. The results show that the formation of the weld is good in a reasonable welding process. Along the fusion line, there are so fine equiaxed grains, and there exist a large number of equiaxed dendritic crystals and columnar grains in the center of the weld. The micro segregation of the weld is more serious at the grain boundaries, such as Cu, Mg and Si, but the Al elements are less. The main reinforcement phase T1 (Al2CuLi) in the weld are almost all disappeared, and there is a certain amount of TB (Al7Cu4Li) phase precipitation. There are a large number of binary eutectics and ternary eutectics in the grain boundary, more Cu5Si and AlCuxMnx brittle compounds. In the heat affected zone (HAZ), the grain size and the size of the second phase become larger. T1 (Al2CuLi), θ" (Al2Cu) and TB phases are undissolved. Under the optimum process, the hardness of the weld zone is the smallest, with an average of 98.6HV, about 65% of the base metal. The tensile strength of the joint is 354MPa, and the elongation is 4.9%, about 67% and 40.8% of the base metal respectively. The tensile fracture occurs preferentially in the coarse equiaxed grain zone at the upper part of the weld, and gradually extends along the grain boundaries, finally fractured in the columnar grain zone. The fracture morphology belongs to the mixed fracture of toughness and brittleness with a large number of dimples.

Key words:2060 Al Li alloy; Laser welding; Microstructure; Mechanical property