The retrogression and re-aging (RRA) processes, aimed mainly at tailoring intergranular precipitates, could significantly improve the corrosion resistance (i.e., stress corrosion cracking resistance) without considerably decreasing the strength, which signifies that an efficient control of the size, distribution and evolution of intergranular and intragranular precipitates becomes critical for the integrated properties of the (mid-)thick high-strength Al alloy plates. Compared to RRA process with retrogression at 200 °C (T77), this study investigated the impact of a modified RRA process (MT77) with lower retrogression temperatures (155-175 °C) and first-stage under-aging on the properties of a high-strength AA7050 Al alloy, in combination with detailed precipitate characterization. The study showed that the strength/microhardness of the RRA-treated alloys decreased with raising retrogression temperature and/or prolonging retrogression time, along with the increased electrical conductivity. The rapid responsiveness of microstructure/property typical of retrogression at 200 °C was obviously postponed or decreased by using MT77 process with longer retrogression time that was more suitable for treating the (mid-)thick plates. On the other hand, higher retrogression temperature facilitated more intragranular η precipitates, coarse intergranular precipitates and wide precipitate free zones, which prominently increased the electrical conductivity alongside a considerable strength loss as compared to the MT77-treated alloys. With the preferred MT77 process, the high strength approaching T6 level as well as good corrosion resistance was achieved. However, though a relatively homogeneous through-thickness strength was obtained, some small discrepancies of properties between the central and surface areas of an 86-mm thick 7050 Al alloy plate were observed, possibly related to the quenching sensitivity. The precipitate evolution and mechanistic connection to the properties were discussed and reviewed for high-strength Al alloys along with suggestions for further RRA optimization.

The intergranular corrosion (IGC) resistance of age-hardening Al–Mg–Si–Cu alloys is closely related to the precipitation behavior adjacent to grain boundaries. In this study, we proposed to regulate the interaction of solute atoms and solute partitioning of Zn-containing Al–Mg–xSi–Cu alloys by introducing dislocations, which can synergistically decorate the intergranular and intragranular precipitation behavior. Consequently, the continuity of grain boundary precipitates and width of solute-depleted precipitate-free zones are inhibited accompanied with high number density or coarse precipitate in the matrix. As a result, the IGC resistance is greatly improved without strength and ductility loss, and the related mechanism has been proposed.

Hot tearing is one of the most severe and irreversible casting defects for many metallic materials. In 2004, Eskin et al. published a review paper in which the development of hot tearing of aluminium alloys was evaluated (Eskin and Suyitno, 2004). Sixteen years have passed and this domain has undergone considerable development. Nevertheless, an updated systematic description of this field has not been presented. Therefore, this article presents the latest research status of the hot tearing during the casting of aluminium alloys. The first part explains the hot tearing phenomenon and its occurrence mechanism. The second part presents a detailed description and analysis of the characterisation methods of the mushy zone mechanical properties and hot tearing susceptibility. The third part presents considerable data pertaining to the mushy zone behaviour, including those of the linear contraction and load behaviour during solidification, semi-solid strength and ductility, and characteristic points related to hot tearing. The fourth part examines the effect of the composition and casting process parameters on the hot tearing susceptibility of aluminium alloys. The fifth part describes the hot tearing simulations and the associated criteria and mechanisms. Finally, recommendations for the further development of hot tearing research are presented.

The effects of vanadium content on the microstructural and mechanical properties of a newly developed hot-work die steel (MPS700V) at room and elevated temperatures have been investigated in this paper. It shows that the ultimate tensile strength (UTS) of MPS700V at room temperature and 700 °C are both strongly dependent on the V content. With the increase of V content from 0 to 1.2% V, The UTS at room temperature increases from 1127 MPa to 1442 MPa, and the UTS at 700 °C increases from 400 MPa to 550 MPa. The transmission electron microscope (TEM) shows that the addition of V is beneficial to increase the nucleation rate and volume fraction of MC nano-carbides during the tempering process, and the size of the MC nano-carbides decreases with the increase of V content. The addition of V also increases the thermal stability of MC nano-carbides at 700 °C, which can be related to the reducing the interface mismatch between MC and matrix. Furthermore, a transformation from Orowan bypass strengthening mechanism to shearing strengthening mechanism caused by the V addition is proposed based on the theoretical analysis and TEM observation.