Abstract
Macroscopic surface morphology and balling mechanism of AZ61 magnesium alloy prepared by Selective laser melting (SLM) have been investigated. This article studied and analyzed the surface morphology and balling phenomenon of Mg in the laser processing from the aspects of Mg inherent metal properties and laser processing. In terms of laser processing, the results show that, in the direction of increasing scanning speed, the energy density decreases, and the phenomenon of balling and porosity on the surface of the magnesium alloy is serious. When the energy density is 133.9–187.5 J/mm3, balling particles are significantly reduced. It can be seen from the low-magnification SEM image that, even at a scanning speed of 250 mm/s (Ev is 187.5 J/mm3), there are still a few small-sized balling particles on the surface. Therefore, in terms of inherent metal properties, the wettability, capillary instability, thermodynamic, and kinetic analysis of the balling behavior of Mg and other metal (Al, Fe, Cu, Ni, Ti) droplets in the SLM process has been carried out, and the dynamic model of magnesium droplet spreading/solidification was established basic on the result of experiment and metal inherent properties. The results show that SLMed magnesium alloy is a competitive process of melt diffusion and solidification. The final result depends on the intrinsic properties of the magnesium alloy and the applied laser processing parameters. The spreading process of Mg melt is very fast. Although the solidification time of Mg melts changes slowly with the increase of metal droplet temperature, the spreading speed is still very fast due to the low melt density, so the balling phenomenon of SLMed Mg can be controlled to a certain extent. Theoretically calculated, the solidification time of Mg melt droplet is longer than the wetting time at 1173 K (900 °C), so the spreading process is dominant, which can minimize the balling and realize the densification of SLMed Mg. The dynamic spreading of molten pool, the analysis of wetting and solidification process, and the establishment of SLM balling model can provide reference for the design of the SLM forming parameters of Mg and other different metals.
Highlights
Magnesium and its alloys meet the needs of high efficiency and sustainable development.Magnesium alloy, as one of the advanced metal materials, is widely used in aerospace, automobile manufacturing, biomedicine, and other industries due to its advantages of high specific strength and light weight [1,2,3]
With the continuous expansion of the application field of advanced magnesium alloy materials, the complex structure, efficient and environmentally friendly production requirements have become the focus of the development of magnesium alloys, so new magnesium alloy preparation technologies have emerged at the historic moment
48 μm, and the particle size distribution is between 30 μm to 70 μm (Figure 1), and it is measured by the laser particle size analyzer LMS-30
Summary
Magnesium and its alloys meet the needs of high efficiency and sustainable development. As one of the advanced metal materials, is widely used in aerospace, automobile manufacturing, biomedicine, and other industries due to its advantages of high specific strength and light weight [1,2,3]. There is the potential and possibility to replace aluminum and steel in many structural applications [4]. These advantages of magnesium and its alloys still have many difficulties to overcome in industrial applications. Materials 2020, 13, 3632 tensile properties (strength and ductility), and corrosion resistance of magnesium alloys. With the continuous expansion of the application field of advanced magnesium alloy materials, the complex structure, efficient and environmentally friendly production requirements have become the focus of the development of magnesium alloys, so new magnesium alloy preparation technologies have emerged at the historic moment
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