The development of Alumina-Forming Austenitic (AFA) stainless steel is reviewed in this paper. As a new type of heat-resistant steel, AFA steel forms an alumina protective scale instead of chromia in a corrosive environment. This work summarizes the types of developed AFA steels and introduces the methods of composition design. Various precipitates appear in the microstructure that directly determine the performance at high temperatures. It was found that alloy elements and the heat treatment process have an important influence on precipitates. In addition, the corrosion resistance of AFA steel in different corrosive environments is systematically analyzed, and the beneficial or harmful effects of different elements on the formation of alumina protective scale are discussed. In this paper, the short-term mechanical properties, creep properties and influencing factors of AFA steel are also analyzed. This work aims to summarize the research status on this subject, analyze the current research results, and explore future research directions.

Ti/Al laminated composite fabricated by explosive welding has received widespread attention due to their potential in achieving excellent performance. However, investigations on the crack evolution and fracture behavior were still limited. In this paper, the morphology and elemental distribution of the bonding interface were investigated. And the crack initiation and propagation of Ti/Al laminated composite was investigated by in-situ tensile test. It is shown that local melted zone (LMZ) was formed along the wavy interface, which was mainly consisted of TiAl2 + TiAl3 intermetallic compounds. The brittle intermetallic compounds on the LMZs are places where cracks initiate. As the internal stress accumulation, cracks generate at the tip of the wavy interface where the Ti layer is thinnest, and they locally form delamination along the interface. Subsequently, the crack tip is released from the Ti layer, leading to a catastrophic fracture to the whole Ti layer. Finally, the crack propagates to the Al layer until the material eventually fractured. Graphical Abstract

Anisotropy is the difference in the microstructure or mechanical properties of materials in different directions. Anisotropic behavior occurs in rolled sheets, and this anisotropy is very obvious in laminated composites. In this work, the influence of anisotropy on the microstructure and mechanical properties of Ti/Al laminated composites fabricated by rolling was investigated. The results show that the microstructure and mechanical properties of the Ti/Al laminated composites were obviously anisotropic. The grains in the Al layer of the composites were elongated along the rolling direction and were compressed perpendicular to the rolling direction. The grains in the Ti layer of the composites had no obvious preferential orientation and comprised mainly twins. With the rolling direction as 0°, the mechanical properties of the Ti/Al laminated composites varied greatly as the angle of the composites increased. The tensile strength, elongation and bond strength of the Ti/Al laminated composites decreased with increasing angle of the composites. In addition, the microhardness of the Ti/Al laminated composites increased with increasing angle of the composites.

As a kind of special energy field assisted plastic forming, electric pulse assisted plastic forming combines multiple physical fields, such as thermal, electrical, magnetic and mechanical effects, has multiple effects on metal. It has a good industrial application prospect in the fields of directional microstructure regulation of materials and preparation of new materials. The flow stress of metal materials can be effectively reduced by electro-pulse assisted forming. The action mechanism of pulse current includes thermodynamics (Joule heating effect) and kinetic (pure electro-plastic effect or athermal effect). Thermodynamically, electric pulses can be used to provide the energy for dislocation migration and atomic diffusion, and aid in microstructure changes such as recrystallization, phase transition and microcrack healing of metals. In terms of dynamics, electric pulse has an effect on the speed and path of dislocation structure evolution. On this basis, a series of theoretical models for accurately predicting the flow stress of materials in electrically assisted forming process were formulated by combining the stress–strain constitutive relationship considering the temperature rise effect and the pure electro-plastic effect. The accuracy of the predicting model is greatly enhanced by the introduction of electrical parameters. The mechanism for electrically assisted forming was further revealed.