Abstract
Al 7050 is not a friendly alloy for laser additive manufacturing because of the presence of low boiling point elements such as Mg and Zn in 7XXX alloys. This paper presents an alternate solution of laser metal deposition of Al 7050 alloy powder coated with nickel. Microstructural investigation using optical and electron microscopy revealed that the deposits are free from relevant defects such as porosity or lack of fusion. However, the added nickel was partially segregated in the inter-dendritic boundaries and formed brittle Al3Ni intermetallics. As a result, as-deposited Ni coated Al 7050 alloy showed almost no tensile ductility. Laser deposited samples were friction stir processed to refine and uniformly distribute Al3Ni particles in the α-Al matrix. Tensile test results revealed a good combination of yield strength (178 MPa), UTS (302 MPa), and 6% elongation of friction stir processed (FSP) samples. Post FSP heat treatment additionally improved both strength and elongation about 10%. Microstructural investigation revealed a systematic change of columnar to equiaxed dendrites from bottom to top of each deposited layer.
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