Research On DC Double Pulse MIG Welding Test Of Al-Mg Composite Panel And Quality Control

Performance lightweight compound material,Al-Mg compound plate plays an important role in weapon armor lightweight applications. The welding technic of compound joint between Al and Mg involve in the problem of welding aluminum layer, magnesium layer and the transition layer between. In the transition layer, the hard and brittle Intermetallic compound emerged, which will raising the difficulty of the weld. In the paper, a new process of double pulse MIG welding between 7A52 aluminum alloy and AZ31B magnesium allay was experimented, exploring the molding technics and interface properties, trying to ascertain the rules which influence the compound weld joint between Al and Mg.The experiment was run in three parts, i.e.7A52 aluminum alloy butt joint via double pulse MIG welding, AZ31B magnesium alloy via double pulse MIG welding and the compound joint between 7A52 aluminum alloy and AZ31B magnesium alloy.The 6mm 7A52 aluminum alloy sheet butt joint was experimented first. Comparing between single pulse mode and double pulse mode, we found that when the welding current is 160A, welding speed is 42cm/min, low-frequency pulse at 5Hz, the weld bead is molded well with low pore rate and a tensile strength at 230Mpa.The 6mm AZ31B magnesium alloy sheet butt joint was experimented followed. Adjusting the welding speed and pulse frequency, we found that when the welding current is 125 welding speed is 55cm/min, low-frequency pulse at 5Hz the weld bead is molded with a tensile strength at 136Mpa, which reaches 90% of the base material.Base on the two experiments above,12mm sheet butt joint welding between 7A52 aluminum alloy and AZ31B magnesium alloy was tested. when the current of Mg-layer is 140A and the current of Al-layer is 200A, a valid metallurgy joint was gained. For the single V groove sample, the proper current is 180A in Al-layer and 125A in Mg-layer. The micro-hardness test revealed that single V groove s hardness at 186.4HV and double V groove at 55HV in the interface.Microscope observing showed that the microstructure of the two kinds of grooves are similar. SEM and EDS analyses showed that the Mg elements diffused heavily to the Al-layer at the interface. In the single V groove, the intermetallic compound layer thickness is 160um, while in the double V groove is 90μm. XRD analyses proved that intermetallic compound is mainly γ phase(Al12Mg17) and β phase(Al3Mg2) with a continuous bond distribution, zinc distributed evenly at the interface without obvious segregation, zinc and magnesium composed a strengthening phase, silicon presented as primary crystal and Mg-Si compound.