On The Plastic Instabilities Phenomenon (Portevin-Le Chatelier Effect) In Al Alloys: Experiments And Theoretical Investigations

In a certain range of temperatures, strain rates and appropriate pre-deformation, many interstitial and substitutional solid solutions may exhibit special plastic instabilities, i.e. serrated flow in stress-strain curves and strain localization in specimen, which is also referred to as the Portevin-Le Chatelier (PLC) effect. The PLC effect is understood as an intrinsic property of materials and generally considered to be a result of dynamic interactions between mobile dislocations and diffusing solute atoms, i.e. the dynamic strain aging (DSA). Aluminum alloys have been widely used due to their high strength-weight ratio and good corrosion resistance, but their formability at room temperature has been severely harmed by the PLC effect in them. Therefore, it is of great significance to study on the PLC effect of Al alloys.By the dynamic digital speckle pattern interferometry (DSPI) technique, the PLC effect in Al alloys is investigated in the present work. Three types of PLC effect, type A, B and C, are distinguished according to their different spatiotemporal aspects. The range of applied strain rates in which each type of PLC effect occurs is obtained for specimens with different thickness. Moreover, the PLC effect manifests itself with versatile spatial aspects, i.e. reversing of band direction, multiple bands emerging simultaneously and the failure process of specimen etc., which are perfectly visualized by the DSPI correlation fringe patterns and qualitatively explained.As the PLC effect is in response to the interactions between dislocation and solute atoms, it is certainly important to investigate the influence of solute concentration on the PLC effect by different heat treatments. In this dissertation, both spatiotemporal aspects in annealed and solution treated LY10 alloys are investigated. And the difference between them is in response to the change of solute concentrations. Influence of natural aging on the critical strain of the PLC effect is also reported, the critical strain is delayed and the PLC effect completely vanishes with increased aging durations.