Laser Metal Deposition of Aluminum 7075 Alloy

Abstract

Additive manufacturing (AM) has become one of the most important research topics with its ability to manufacture a wide range of alloys like steel, nickel-based super alloys, titanium alloys, aluminum alloys, etc. Al 7075 is not a friendly alloy for laser metal deposition (LMD). This paper reports the successful development of LMD process for deposition of defect-free Al 7075 alloy. By preheating the substrate to 260°C the residual stress decreased and eliminated the hot/solidification cracks in the deposit. LMD is a rapid cooling process due to which the gas bubbles of Mg and Zn are trapped in the deposit. These are identified as gas porosity because of the partial evaporation of low boiling point elements like magnesium and zinc present in this alloy. The least porosity observed was 0.08% at 29 J/mm 2 of energy input. The SEM and EDS investigation of as-deposited Al 7075 revealed the segregation of Cu, Mg, and Zn rich phases along the interdendritic regions and grain boundaries. Cu, Mg, and Zn rich phases at the interdendritic regions dissolved into the α-Almatrix after heat treatment. The XRD scan of laser deposited Al 7075 revealed the presence of Al 2 CuMg and MgZn 2 precipitation hardening phases.

Novel Assessment Methodology for Laser Metal Deposition of New Metallic Alloys

“…The sample should not have a large cross-section to concentrate the energy and avoid heat losses through the sample. This is especially important for aluminum alloys due to the high thermal conductivity of the material [ 28 , 29 ]. However, the substrate should have enough height and width to differentiate the molten area from the unaffected zone.…”

“…The experimental procedure of substrate heating was divided into two steps: preheating and melting. The first was conducted to reduce the thermal jump to melt the material, improve the absorptivity so the energy necessary for the melting step was reduced, and reduce the residual stresses during melting [ 28 ]. Absorptivity of aluminum increases with temperature [ 30 , 31 ].…”

“…As a criterion for simulation, it was established not to exceed the evaporation temperature of any alloying element of the AA7075 alloy. Among the different components of the alloy, zinc and magnesium have the lowest evaporation temperature [ 28 ]. Consequently, it was determined that the maximum temperature should not exceed 907 °C at any point on the sample.…”

“…As aluminum powder can be flammable and explosive in the presence of oxygen and a heat source, an inert chamber had to be used to control the oxygen content in the LMD experiments with powder. After a literature search [ 28 , 36 , 37 , 38 , 39 ], it was decided to fabricate an inert chamber with a rigid box and a flexible lid. Eventually, a methacrylate box with an area of 500 × 500 mm 2 and a height of 150 mm was made.…”

Effect of process parameters and grain refinement on hot tearing susceptibility of high strength aluminum alloy 2139 in laser powder bed fusion

“…Hence, the energy density 1721 J/mm 3 can be selected as a preferred key PBF-LB/M parameter for A12139. The loss of Mg during PBF-LB/M at high energy densities is a known issue for high strength Al alloys [41][42][43][44] and is caused by evaporation. Mg has a relatively low evaporation temperature (1090 °C) and the local temperature during PBF-LB/M at high energy densities can well exceed this temperature.…”