Solidification Behaviour and the Evolution of Microstructure in the Laser Cladding of Aluminium on Magnesium Substrate

Abstract

Laser cladding of aluminium powders was performed on pure magnesium substrates using the blown powder method. The microstructure across the laser-clad track was studied. Starting from the bottom of the laser-clad to the top surface of the track, a series of microstructures was observed: a planar growth interface of the substrate, a narrow band of ( þ ) eutectic, a narrow band of cellular structure, and finally a relatively thick layer of -Al and ( þ ) eutectic structure. The evolution of the various phases and microstructures is discussed in terms of the distribution of solute in conjunction with the Al-Mg phase diagram, temperature gradient and solidification rate, constitutional supercooling theory, and the condition for columnar-to-equiaxed crystal transition.

Microstructure development in laser forming of zirconium coatings on AZ91D magnesium alloy substrates

“…6, reveals that the Zr rich dendrites appear in white, while the compounds of Zr 4 Al 3 and Zr 3 Al 2 , are in dark grey. The former was growing from the bottom of the Zr layer in a direction towards the substrate over a distance of about 5-10 m. Such a backward cellular growth phenomenon in laser deposition has been reported by the author previously [15], and was attributed to the presence of a relatively low melting point liquid phase existing at the substrate interface, and the situation is similar to the present case.…”

Phase evolution and dendrite growth in laser cladding of aluminium on zirconium

“…Moreover, it has excellent corrosion resistance in salt-laden environments [8]. This paper forms part of a wider study that investigates laser cladding of graded Zr/Al coatings on Mg substrates, and focuses on studying phase evolution in the rapid solidification of Al on Zr; while the study of the solidification behaviour and the evolution of the microstructure in laser cladding of aluminium on magnesium substrates has been reported previously [9]. …”

Growth Morphology of CuMg2 in Laser Forming of AlCoCrCuFeNi Coating on Mg

“…Later, Cahn and coauthors [13] proposed that a faceted-to-non-faceted transition will always occur at some undercooling. Since the CuMg 2 dendrites are located within the composite layer, during the solidification, the undercooling at the dendrite front is given by [14]  ∆VC 0 /A  where V is the solidification velocity, C 0 is the given composition and A is the constant. According to Equation (1), the undercooling increases with the solidification velocity increasing.…”