Design, friction stir processing and characterization of a new healable aluminium alloy

Aluminium alloys are widely used as structural materials in transportation, space and construction. Despite the excellent combination of lightweight with sufficient strength, to remain competitive on the market, several properties of Al alloys should be further enhanced, such as strength and damage tolerance. One way to improve the strength of Al alloys is to combine them with reinforcements, thus processing Aluminium matrix composites (AMCs). These materials present several advantages compared to Al alloys, such as higher strength, elevated temperature resistance and lower thermal expansion coefficient. In addition, to improve damage tolerance of Al alloys and AMCs, Friction Stir Processing (FSP) can be used. However, the classical approach of damage prevention is not the only solution to improve damage tolerance and meet materials sustainability requirements. Instead, damage management approach can be used to achieve alloys longevity, among which self-healing strategies are promissing approaches. In the present study, a new healable Al based composite presenting healing behaviour was produced by FSP. A new Programmed Damage and Repair (PDR) healing concept was proposed. In this concept, the damage provoked by the load appears on sacrificial particles. When the selected healing heat treatment is applied, healing occurs using the matrix atoms as a healing source. Healing was demonstrated using in-situ heating under 3D nanoholotomography and TEM. It was shown that heating this material for 10 min at 400 °C is sufficient to heal incipient damage with complete filling of 70% of all damage (and up to 90% when its initial size is below 0.2 μm). Furthermore, strength is retained and the work of fracture of the alloy is improved by about 40% after healing. A study of the effect of alloy composition on the healing efficiency and work of fracture opens new path for optimizing this PDR alloy.(FSA - Sciences de l'ingénieur) -- UCL, 202