A weld cross-section with corresponding thermal histories in the weld metal and heat-affected zone. Below are typical hardness profiles induced across welds in heat-treatable aluminum alloys, low-carbon steel and low-alloy steel.
Welding metallurgy is a big field of study—welds are often the ‘Achilles heel’ in design, being the critical locations that determine failure and allowable stresses. This may be in part because the material properties are damaged in some wayat the joint (as in this example), but it may also be due to other side-effects of the process (residual stresses, or stress concentrations, or crevices, potentially causing fatigue and corrosion problems). Adhesive technologies are not trouble free—they still concentrate stress and contain defects, requiring good design and process control—but they have the advantage that they don’t impose heat or deformation on the components being joined, leaving the microstructure and properties intact.
