Fusion Zone Shapes in Electron-Beam Welding Dissimilar Metals

Experiments on welding dissimilar metals, such as aluminum or copper to iron with an electron-beam welder, are conducted. It is found that the observed depth-to-width ratio of the fusion zone in aluminum can be greater than unity while that in iron is around unity. The former is attributed to the formation of a cavity resulting from a high vapor pressure. The difference in depths increases with beam power. The observed depth-to-width ratios of fusion zones in welding copper to iron can be greater than unity. A unique maximum depth is near the joint plane, as a result of strong convective mixing and high incident flux, even though the melting temperatures are different. Strong mixing is confirmed by measured concentration profiles across the fusion zones of dissimilar metals. To a first approximation fusion zone depths with depth-to-width ratios greater than or identical to unity are determined from scale analyses of heat conduction equations in welding the same metals with a high and low-power-density beam, respectively. The propositions are verified by experimental results. [S0022-1481(00)00103-1]