Mechanical surface treatments of lightweight materials - Effects on fatigue strength and near-surface microstructures

Mechanical surface treatments such as shot peening or deep rolling are well -known processes to improve the fatigue strength of metallic components. Th is is due to favorable microstructural alterations in relatively thin surfa ce layers as a consequence of near-surface inhomogeneous plastic deformatio ns. Typical examples demonstrate the fatigue-strength increase for mechanic ally surface-treated specimens. Existing possibilities to improve the fatig ue strength of welded joints by mechanical surface treatments are also incl uded. In the case of lightweight materials (e. g. magnesium- or aluminum-ba se alloys), process parameters must be well adapted in individual cases to achieve optimum near-surface material states, taking into account the wide range of mechanical properties attainable as a result of their specific mat erial microstructure. The effects of process parameters and microstructures on near-surface mater ials properties resulting from mechanical surface treatments are demonstrat ed with examples. Depth distributions of macroresidual and microresidual st resses are analyzed together with microstructural observations. An importan t point for the effectiveness of mechanical surface treatments is the stabi lity of the near-surface material states during loading history. This aspec t is treated for the case of fatigue loading.