Abstract
Porosity is reported to be a major issue when welding cast magnesium. Therefore, it is important to understand the pore formation mechanisms and find procedures that could be used to reduce porosity. This study investigated the possibility of using twin-spot optics for reducing the porosity in laser welded cast magnesium. Two twin-spot welding setups were compared using either a beam splitter or twin-spot welding with primary and secondary (placed in front of the primary optic) optics. The results showed that welding with a dual optic setup with a defocused secondary beam reduced the volumetric porosity in the weld to 5%. The highest levels of volumetric porosity were 30%, and were a result of using the dual optic setup, but with a defocused primary beam. No clear relation between the level of porosity and power or welding speed was found. It was found that the amount of porosity depended on the balance of the energy input (controlled by defocusing) between the two beams. Porosity formation can be reduced if the energy from the first beam results in the nucleation and initial growth of pores. Reheating by the second beam then allows the pores to grow and escape from the molten material without melting additional base material. Furthermore, twin-spot welding is shown to be a promising combination of a production friendly solution and high quality welding.
Highlights
IntroductionCompared with high strength steel and aluminium, magnesium alloys provide
In the figure it is clear that twin-spot welding with a beam splitter does not result in a lower porosity amount compared with single-spot welding
Full penetration bead-on-plate welds were produced by laser twin-spot welded in the magnesium alloy AM50 to study pore formation
Summary
Compared with high strength steel and aluminium, magnesium alloys provide. Magnesium alloys are suitable for automotive and aerospace industry. The tensile strength of these alloys has a rather low range of 190 - 310 MPa, which limits suitable applications; to e.g. seat frames, steering wheels or structural dashboard cross beams [1] [2] [3] [4]. The advantages of AM50 compared with most other magnesium alloys are its higher strength, higher hardness, high elongation and excellent castability, which makes it a good candidate for light weight structures [5]
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