The materials with grain size gradient variation on the surface, which were prepared with mechanical-induced severe plastic deformation, always show high resistance to high and low cycle fatigue and frictional wear because of their good strength–ductility synergy. The ultrasonic surface rolling treatment (USRT) has the advantages of high processing efficiency, good surface quality, and large residual compressive stress introduced to the surface after treatment. The USRT was used to prepare aluminum alloy (AA7075) samples with a surface gradient structure; meanwhile, the microstructural evolution mechanism of the deformation layers on the gradient structure was studied with XRD, SEM, and TEM. The microstructure with gradient distribution of grain size and dislocation density formed on the surface of AA7075 aluminum alloy after USRT. The surface layer consists of nanocrystals with random orientation distribution, and high-density dislocation cells and subgrains formed in some grains in the subsurface layer, while the center of the material is an undeformed coarse-grained matrix. The results show that the dislocation slip dominates the grain refinement process, following the continuous cutting and refinement of dislocation cells, subgrains, and fragmentation of the second precipitates. This study systematically clarified the mechanism of grain refinement and nanocrystallization on the surface of high-strength aluminum alloys and laid a theoretical foundation for further research on mechanical behavior and surface friction and wear properties of high-strength non-ferrous materials with gradient structure.

Here, the corrosion weight-loss method, surface analysis technology, and electrochemical test methods were used to study the corrosion behavior and electrochemical characteristics of experimental samples of Q345R steel in a sterile solution (pH 2.0) and a solution containing T. ferrooxidans. The growth cycle of T. ferrooxidans was determined to be approximately 8 days. The corrosion weight-loss method showed that the corrosion rate of Q345R carbon steel coupons decreased with time in the T. ferrooxidans system and the sterile system; the corrosion rate was approximately two times higher in the T. ferrooxidans system than in the sterile system. The corrosion morphology results showed that the presence of T. ferrooxidans promotes the corrosion of Q345R steel and increases the local corrosion of the matrix material. The electrochemical test results showed that after 5 days of corrosion, the polarization resistance of the T. ferrooxidans system was approximately 50% of that of the sterile system, and the corrosion current density of the T. ferrooxidans system was approximately twice as high as that of the sterile system. Therefore, T. ferrooxidans can accelerate the corrosion of Q345R steel two-fold.

Ecological restoration of alpine sandy lands plays an important role in promoting vegetation recovery and enhancing ecosystem functions. However, the response characteristics of plant functional groups and nitrogen (N) and phosphorus (P) dynamics under different restoration treatments remain unclear. Taking three typical ecological restoration treatments in the alpine semi-humid sandy land on the eastern edge of the Qinghai–Tibet Plateau—fencing + sand barrier establishment + mixed grass seeding (MG), fencing + sand barrier establishment + shrub planting alone (SA), and fencing + sand barrier establishment + shrub–grass combination (SG)—as the study objects, and unrestored natural sandy land as the control (CK), this study investigated the characteristics of plant biomass and diversity, as well as the content and stoichiometric characteristics of N and P in the plant–litter system under different restoration treatments, and analyzed the response relationships between plant diversity and changes in N and P in the plant–litter system. The results showed that all three restoration treatments increased plant community biomass and diversity indices. Among them, the SG treatment had the highest aboveground biomass and diversity, whereas the MG treatment had the largest belowground biomass. All three restoration treatments increased the N and P contents of herbaceous plants and litter, with the greatest increases observed under the SG treatment. The results for plant functional groups showed that legumes had the highest N content, while forbs had the highest P content. The N:P ratios of aboveground plant parts ranged from 5.85 to 8.82 and were lower in the SA and SG treatments, suggesting that plants under the restoration treatments may be N-limited. In conclusion, the SG treatment is the most effective restoration approach for promoting vegetation recovery and nutrient content in alpine sandy lands. These results provide a scientific basis for selecting ecological restoration treatments for alpine sandy lands and for improving restoration effectiveness and efficiency.