Weldability of Nickel/Aluminum Dissimilar Materials Laser Welding Part II: Microstructure Development, Solidification Behavior and Mechanical Properties of Polycrystalline Aluminum Alloy

Abstract

The weldability and fabricability of nonheat treatable Aluminum-Magnesium alloy 5083H116 in shipbuilding industry by attractive laser welding are progressively assessed in this paper. The response of crack-resistant microstructure development, phase transformation and mechanical properties to energy input is very sensitive and distinguishable during laser welding process. Supersaturation of α-Al solid solution is prominently released by granular Al3Mg2 β phase during rapid solidification. Keyhole weld profile leads to parabolic-shaped distributions of alloying components and nonequilibrium β phase. Heat flow and solute elements are thermometallurgically accumulated in neck region, where maximum β phase and alloying element cluster are located. Asymmetrically, amount of Magnesium-rich β phase in the left portion of weld is the largest, dispersive β phase nearby weld center softening region is the lowest, where mechanical properties are worst, and diffusion-limited β phase in the right side is intermediate. There is significant discrepancy between left side, right side and center part of weld in solute redistribution and β/α eutectic phase transformation, which substantially contribute to obvious tensile properties fluctuation. Nucleation and growth of a few β phase particles in the dimple heterogeneously weaken weld integrity and are detrimental to weld strength and ductility. Weld specimens ductilely fracture in the center part, and plastically experience much deformation. Fracture surface morphologies show plenty of large and deep dimples after intense plastic deformation. Loss of strengthening elements and hydrogen-related porosity are attributed to evaporation-dependent weld pool instability. Additionally, the eutectic-driven microstructure analysis results are in consonance with mechanical behavior. The internal temperature development, molten pool duration, solid/liquid interface location, heat dissipation and weld quality should be appositely balanced by processing variables rearrangement.