The precipitates and properties evolution behaviors of AlZnMgCu alloy during the retrogression process with slow heating

In order to develop the retrogression and re-aging (RRA) effect on the performance of AlZnMgCu alloy products with large scale, the hardness, electrical conductivity, tensile properties, and exfoliation corrosion resistance of the Al7.7Zn2.1Mg2.0Cu alloy were investigated at two pre-aging temperatures and a 3 °C/min retrogression heating rate. Transmission electron microscopy (TEM) was used to investigate the evolutions of precipitates at different RRA routes. Results revealed that the standard compliant performances could also achieved by setting the pre-aging as the under-aged state when the slow retrogression heating rate existed. Continuous precipitation occurred at the early stage of heating retrogression. The dissolution behavior of the GP zone with the radius lower than the critical value had finished in heating retrogression. The η′ phase re-precipitated firstly in the isothermal retrogression, then grew and coarsened with the retrogression time increase. During the whole retrogression including heating and isothermal stages, the hardness undergone an “up-down-up-down” transversion. After RRA-treated at (105 °C, 24 h + (heating to 190 °C at 3 °C/min)190 °C, 50 min +120 °C, 24 h), excellent corrosion resistance achieved with only a 5.5% sacrifice of tensile strength when compared to peak aged state. Due to the slow temperature-rising process in retrogression for the large section products, the optimized RRA schedule is more practical for industrial applications

Inhomogeneity of Microstructure and Properties of 7085-T651 Aluminum Alloy Extra-thick Plate

Inhomogeneity of microstructure and properties of 7085-T651 aluminum alloy extra-thick plate were investigated by tensile properties, exfoliation corrosion, optical microscopy(OM), composition analysis, scanning electron microscopy(SEM),differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results show that the microstructure, tensile property and exfoliation corrosion in different layers of 7085-T651 aluminum alloy of 110 mm thick are inhomogeneous. For the 1/4 thickness layer, the tensile strength is the minimum, 540 MPa, and the resistance to exfoliation corrosion of this layer is the worst, with exfoliation corrosion classification of EB. For the core layer, the tensile strength is the maximum, 580 MPa. The resistance to exfoliation corrosion of the surface layer is the best, with exfoliation corrosion classification of EA. For the 1/4 thickness layer, it has the largest recrystallized fraction up to about 47.7% and the grain size is about 105 μm; there are equilibrium phase particles precipitated on grain boundaries or within grains; the size of aging precipitates is small; and thus both mechanical properties and resistance to exfoliation corrosion are the worst. For the core layer, it has the smallest recrystallized fraction of about 14.8% and there are a large amount of sub-grains; the fraction of residual phase Al7Cu2Fe almost reaches up to about 1.43%; the size of the equilibrium phase on grain boundaries, the size of aging precipitates and the width of PFZ are large, and therefore good mechanical properties and bad resistance to exfoliation corrosion are obtained

Hydrogen-induced failure in a partially-recrystallized Al-Zn-Mg-Cu alloy with different aging conditions: Influence of deformation behavior dominated by microstructures

Hydrogen-induced failure in a partially-recrystallized Al-Zn-Mg-Cu alloy with different aging conditions was studied by in-situ electrochemical hydrogen charging method, and the hydrogen-induced cracking mechanism was elucidated by investigating the microstructure-dominated deformation behavior. It was found that in naturally-aged and peak-aged samples, cracks initiate at sample surfaces, and deformation dominated by shearing facilitates hydrogen diffusion, resulting in a high hydrogen embrittlement susceptibility. However, in the over-aged sample, deformation dominated by bypassing cannot transport hydrogen efficiently, which exerts no effect on crack initiation at the sample center. In addition, the same cracking pattern exists on all samples in silicone oil and in-situ hydrogen charging environments. The grain boundary of recrystallized grains is prone to strain localization, leading to intergranular cracking. In unrecrystallized grains, transgranular cracks propagate along intersections of slip lines and subgrain boundaries. This study improves the understanding of hydrogen embrittlement in new generation Al-Zn-Mg-Cu alloy by linking the existing hydrogen embrittlement mechanism to the deformation behavior dominated by microstructures

Niche conservatism and elevated diversification shape species diversity in drylands: evidence from Zygophyllaceae

The integrated contributions of climate and macroevolutionary processes to global patterns of species diversity are still controversial in spite of a long history of studies. The niche conservatism hypothesis and the net diversification rate hypothesis have gained wide attention in recent literature. Many studies have tested these two hypotheses for woody species in humid forests; however, the determinants of species diversity patterns for arid-adapted plants remain largely ignored. Here, using a molecular phylogeny and the global distributions of Zygophyllaceae, a typical arid-adapted plant family, we assessed the effects of contemporary climate and net diversification rates on species diversity patterns in drylands. We found the variables representing water availability to be the best predictors for Zygophyllaceae diversity. Specifically, Zygophyllaceae species diversity significantly decreased with the increase in water availability, probably owing to phylogenetic conservatism of water-related niches. The net diversification rates of Zygophyllaceae accelerated sharply in the recent 10 Myr, coinciding roughly with the period of global aridification. The species diversity of Zygophyllaceae significantly increased with the increase in mean net diversification rates per geographical unit, especially in the OldWorld, supporting the net diversification rate hypothesis. Our study provides a case exploring climatic and evolutionary mechanisms of dryland species diversity patterns, and suggests that the conservatism in water-related niches and elevated net diversification rates in drylands may have jointly determined the global patterns of dryland species diversity