Control of Magnesium Loss During Laser Welding of Al-5083 Using a Plasma Suppression Technique

A major problem of autogeneous laser welding Al-5083 is the loss of magnesium by evaporation or plasma formation. This consequently results in welds of low tensile strength and unacceptable porosity. A method has been developed to control plasma formation during welding resulting in satisfactory welds with little or no magnesium loss and porosity. Plasma formation was controlled by manipulation of a main gas jet in a shielding arrangement during welding. Shielding gas pressure needed to suppress the plasma was within an order of magnitude of the theoretically estimated pressure required to sustain a vapor filled “keyhole.” The experiment was carried out using a 10 kW CW-CO₂ laser. A two-level factorial experimental design correlated the effects of the independent laser processing variables with as-welded alloy chemistry. Alloy composition was characterized quantitatively using electron probe microanalysis techniques. Observations revealed that magnesium loss could be minimized to as low as 0.9 percent. Radiographic examination and tensile tests further demonstrated that low porosity welds with strengths at least as great as the parent material may be produced by controlling alloy composition via a specially designed inert gas shield.