Microstructure and corrosion characteristics of laser-alloyed magnesium alloy AZ91D with Al–Si powder

Figures & data

Nominal compositions of magnesium alloy AZ91D (wt.%).

Al	Zn	Mn	Si	Fe	Cu	Ni	Mg
8.84	0.82	0.12	0.02	0.0004	0.002	0.0006	Balance

Figure 1 Microstructures of as-cast magnesium alloy AZ91D. (a) Matrix α-Mg solid solution with segregated γ-Mg₁₇Al₁₂ IMCs along grain boundaries and (b) grain boundary γ-Mg₁₇Al₁₂ and some eutectics.

Figure 2 Morphology and microstructure of alloyed AZ91D layer: (a) transection view; (b) narrow HAZ and liquified γ-Al₁₂Mg₁₇ IMCs; (c) dendritic and angular IMC phases; (d) upper region of (c) featuring compact structure of phases.

Figure 3 Hardness distributioin of laser-alloyed AZ91D layer with Al–Si.

Figure 4 XRD spectrum of laser-alloyed AZ91D layer with Al–Si powder.

Figure 5 Polarization curve of Al–Si alloyed layers and AZ91D in 3.5 wt.% NaCl solution.

Figure 6 Corrosion features of AZ91D base metal in 3.5% NaCl solution: (a) preferential corrosion sites and (b) preferential attack at α-magnesium solid solution leaving grain boundary γ-Al₁₂Mg₁₇ unattacked.

Figure 7 Corrosion features of Al–Si alloyed AZ91D layer in 3.5% NaCl solution. (a) General view; (b) central area of (a); (c) details of A-I showing preferential attack at matrix of α-Mg and Al solid solution; (d) details at A-II showing early interfacial attack at the interface of IMCs (arrows).

Figure 8 Preferential corrosion of Al–Si alloyed AZ91D microstructure. (a) Corroded microgrooves in substructures of matrix (lighter particles are either Al₁₂Mg₁₇ or Al₃Mg₂). (b) IMC phases hanging over corroded concave matrix.