Effect of Mg admixing on strength and corrosion of electron beam additive manufactured AlSi12 on the AA5056 substrate

Electron beam additive wire feed manufacturing has been applied for depositing AlSi12 layers on the AA5056 substrate to form a wall. The accelerating voltage and horizontal deposition speed were kept constant at 30 kV and 375 mm/min, respectively, while the heat input was changed by exponentially changing the beam current from 25 mA when depositing the first layers on a substrate to 18 mA when depositing the last top layers. Three structurally different zones have been obtained depending upon the multilayer sample. Microstructure, microhardness, corrosion resistance, phase and elemental composition of these zones have been investigated. The layer-by-layer deposition strategy resulted in admixing Mg from the melted AA5056 into transition zone as well as into as-deposited AlSi12 layers. The resulting as-deposited AlSi12 alloy structure was represented by α-Al dendrites and α-Al + Si eutectics with fine Mg2Si particles. The transition zone contained α-Al grains with coarse α-Al + Mg2Si eutectics, which had an adverse effect on its corrosion resistance but allowed improving the tensile strength as compared to that of as-deposited AlSi12 whose tensile strength at the level of 207 MPa was determined by microstructure of the deposited AlSi12 layers containing α-Al dendrites, α-Al + Si eutectics and fine Mg2Si precipitates. The as-deposited AlSi12 showed the maximum corrosion resistance with corrosion potential at −545 mV.