The investigation of the oriented precipitate-free zone in high strength aluminum alloy welds
高强铝合金焊接接头无析出物区的形成机理

The microstructure in the partially melted zone of an arc-welded 20mm thickness 2519-T87 high strength aluminum alloy is investigated, an oriented precipitate-free zone is found behind the grain boundary, and this zone is not uniformly surrounding the grain, but usually oriented toward the fusion line. The formation mechanism of this zone is also studied. Results indicate that the mechanism of grain boundary liquid film migration is favored the formation of the precipitate free zone, the driving forces include coherency strain energy, the differential strain energy between the two grains induced by the elastic stresses generated during welding and differential surface energy due to grain boundary curvature. And with the increase of heat input, the thickness of the precipitate free zone increase. The precipitate free zone is harmful to the mechanical property of partially melted zone, and the fractography of PMZ showing the intergranular fracture.