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The AISI 321 steels of structural components serviced at high temperature are usually subjected to oxidation and thermal shock damage during service. Therefore, to improve their high-temperature oxidation and thermal shock resistance, the self-healing coating consisting of Al2O3-13 %TiO2 layer, TiC layer and NiCrAlY layer was prepared for 321 steels in this work. The experimental and microstructural characterization results showed that the thermal shock resistance of such self-healing coating was remarkably improved as compared to the counterpart double-AT13 coating. This is because the volume increment resulting from the oxidation reaction between the TiC and oxygen decreased the porosity of the self-healing coating and retarded crack growth, which also led to the improved high-temperature oxidation resistance. Further, a thermal shock life model based on the crack growth model of Paris formula were developed. The modeling results not only agreed well with the experimental results but also indicated that thickening of thermal grown oxide (TGO) is the main cause of crack initiation and growth.

The usage of Mg–Al–Zn alloys for lithium-ion battery shell is able to achieve further lightweight of electric vehicles, and their corrosion resistance would highly determine the service life. In this work, therefore, a Y-modified AZ91 magnesium alloy (AZ91-0.5Y) was first prepared by conventional casting and following hot extrusion, and the influence of solution treatment (ST) and subsequent pre-deformation (SP) treatments on its electrochemical corrosion and stress corrosion cracking (SCC) resistance in 1 mol/L LiPF6 electrolyte were then investigated. The results indicated that the presence of large lamellar or rod-like β-Mg17Al12 phase in as-extruded AZ91-0.5Y alloy would lead to serious micro-galvanic corrosion and SCC. After solution treatment, the β-Mg17Al12 phase almost completely dissolved into Mg matrix, weakening the micro-galvanic corrosion and anodic dissolution (AD) and hydrogen embrittlement (HE) effect. Further, the subsequent pre-deformation treatment could introduce dislocation, more precipitation of Al2Y phase, massive twins and optimized texture, leading to the improved corrosion resistance and mechanical strength as well as the formation of well-integrated protective corrosion product film MgF2 with low porosity. As a result, the corrosion and SCC resistance of as-extruded, ST and SP specimens is ordered from low to high.

Most industrial hot working operations of heat treatable Al alloys are frequently comprised of several successive deformation stages, and therefore the in-depth understanding and better prediction of flow stress evolution during multi-stage thermomechanical processing are required in modern aluminum industries. In this work, the effects of pre-precipitation microstructures on the complicated flow stress behaviors of an Al-Cu-Mg-Zr alloy during multi-stage hot deformation were first investigated. Further, a new integrated model was developed to predict the multi-stage flow stress behaviors. Concretely, by considering dynamic microstructural evolution, a microstructure-based constitutive KM + Avrami model in which the parameters could be well described by the empirical relationship with the Zener-Hollomon parameter was developed to predict the whole flow stress evolutions of single-stage deformation. Then, a novel approach was proposed to describe the whole flow behaviors during multi-stage hot deformation by integrating the microstructure-based constitutive approaches and a physically-based recovery model for static softening. A good modeling capability and agreement between the modeled and experimental flow stress results was found for the studied alloy with three types of pre-precipitation microstructures. In addition, the in-depth dynamic and static softening mechanisms with the influences of pre-precipitation were also discussed based on modeling analysis and microstructural observations.

The complex precipitation evolutions of Al-Cu-Mg alloys during both non-isothermal and isothermal thermal processes have been found to work on their mechanical properties and electrical resistivity. Modeling of the precipitation kinetics, electrical resistivity and strength evolution is therefore essential for optimizing heat treatment and processing of these alloys. In this work, in situ electrical resistivity monitoring during both non-isothermal and isothermal thermal processes and microstructural characterizations were conducted on an Al-Cu-Mg-Zr alloy with different pre-precipitation microstructures to provide fundamental insights of precipitation behaviors. The results showed that precipitation behaviors of Al-Cu-Mg-Zr alloy, such as the dominant strengthening phase, were highly dependent on pre-precipitation microstructures and thermal history. A time–temperature-microstructure-properties map was established to unravel precipitation characteristics and their strengthening functions. The maximum hardness was indicated to be attributed to the combined presence of Guinier–Preston–Bagaryatsky (GPB) zones and fine S (Al2CuMg) phase. Further, in situ electrical resistivity was used as the main input data to develop an improved model based on the classical Kampmann and Wagner type numerical model (KWN model). This integrated model could not only reveal precipitation kinetics but also well predict hardness evolutions of the studied alloy during non-isothermal and isothermal processes.