Metastable 304 austenitic stainless steel was subjected to rolling at cryogenic and room temperatures, followed by annealing at different temperatures from 500 to 950°C. Phase transition during annealing was studied using X-ray diffractometry. Transmission electron microscopy and electron backscattered diffraction were used to characterize the martensite transformation and the distribution of austenite grain size after annealing. The recrystallization mechanism during cryogenic rolling was a reversal of martensite into austenite and austenite growth. Cryogenic rolling followed by annealing refined grains to 4.7 μm compared with 8.7 μm achieved under room-temperature rolling, as shown by the electron backscattered diffraction images. Tensile tests showed significantly improved mechanical properties after cryogenic rolling as the yield strength was enhanced by 47% compared with room-temperature rolling.

An improved double step hot rolling (DTR) processing was proposed to manufacture fine grained Al–Zn–Mg–Cu alloys based on pre-deformation, short-period annealing and final hot rolling. The DTR processing can produce high-quality rolling sheets with much finer recrystallized structures and significantly improved mechanical properties when compared with the conventional hot rolling (CTR). The main differences between the two TMTs (thermomechanical treatments) were investigated and the specific grain refining procedure of DTR was carefully characterized. The results show that the grain refinement is mainly proceeded via dislocation rearrangement and low angle grain boundaries transition, which can be attributed to the pinning effect of deformation induced precipitates (DIPs). Pre-deformation can accelerate the formation and spheroidization of fine DIPs which prohibit the migration of grain boundaries and the movement of dislocations. As a result, high density dislocation cells are formed and turn into polygon sub-grains after short-period intermediate annealing. During the final hot rolling, low angle grain boundaries gradually transferred into high angle grain boundaries which contributes to the final fine grained structures. The initiation and propagation of cracks were also delayed by grain refinement.

•AZ31/WE43 bimetal composite was prepared by insert molding method.•Interfacial bonding behavior can be dominated by formation of intermetallic phases.•The bimetal composite exhibits large shear strength (108 MPa).AZ31/WE43 bimetal composites are prepared by insert molding method, and the microstructure evolution, phase constitution and bonding strength at the interface are investigated. A relatively uniform transition interface with a thickness of 50 to 150 μm is formed, indicating a good metallurgical bonding. The analysis shows the transition interface is mainly composed of lamellar-like and particulate Al2RE phase, particulate Al3Zr phase on AZ31 side, a precipitation free zone (PFZ) in the middle and quadrate-like Y-rich phases congregated together at the grain boundary close to WE43 side. The average interface shear strength is 108 MPa, which is much superior to other bimetal composites reported so far. The fracture analysis indicates that during the shear tests, the cracks initiates from the weak zone of casting AZ31 alloy. Aided by the interface microstructure, the mechanism on interface bonding is further discussed.

•The improved thermomechanical processing DHR can produce high-quality sheets with finer grains.•Grain refinement is preceeded via dislocation rearrangement and low angle grain boundaries transition.•Fine dispersed matrix precipitates and discontinuous grain boundary precipitates can be obtained by DHR.•DHR can improve tensile plasticity and corrosion resistance.An improved thermomechanical processing double step hot rolling (DHR) was proposed to manufacture fine-grained Al-Zn-Mg-Cu alloys based on pre-deformation, short time intermediate annealing and final hot rolling. The corresponding microstructure evolution, mechanical properties and corrosion resistance were investigated. The DHR processing can produce high-quality sheets with finer grains than the conventional hot rolling (CHR). The grain refinement is mainly proceeded via dislocation rearrangement and low angle grain boundary transition. The grain boundary area (with coarse grains) is small in the CHR alloy and enormous solute atoms could move from intra-granular area to grain boundaries. Therefore, coarse particles precipitated continuously along grain boundaries. However, larger grain boundary area is obtained in DHR alloy by finer grain structures leading to the formation of discontinuous grain boundary precipitates. The results reveal that the present DHR treated alloy possesses improved tensile plasticity and corrosion resistance than the CHR alloy because of refined grains and discontinuous grain boundary precipitates. Thus, the present DHR processing is a promising manufacturing process for obtaining fine grained heat-treatable Al alloy sheets.

•Zn has a negligible influence on the final recrystallization microstructure and texture of Al-Mg-Si-Cu alloys.•By adding Fe-rich phase particles to refine the recrystallization grain sizes could control the texture.•The deep drawability of Al-Mg-Si-Cu alloys could be affected by solute Zn atom besides the microstructure and texture.The effect of Zn on the microstructure, texture evolution and mechanical properties of Al-Mg-Si-Cu alloys with a medium number of Fe-rich phase particles was investigated using tensile testing machine, optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffractometer (XRD) in the present study. The results show that Zn addition has a significant influence on the final mechanical properties, but a slight effect on microstructure and final recrystallization texture. Zn addition is favorable to increase yield strength, ultimate tensile strength and elongation, however it is detrimental to improve r value and reduce Δr value. During the thermomechanical processing, the microstructure almost has nothing to do with Zn addition. However, Zn could prevent the secondary phase particles from precipitating during intermediate annealing. In contrast to the alloy sheet without Zn, the alloy sheet with 1.0 wt% Zn always has weaker textures before final cold rolling, but a stronger texture after experiencing final cold rolling. After solution treatment, they almost possess the same recrystallization texture. Finally, the effect of Zn addition on the recrystallization texture was discussed. Their similar recrystallization texture can be attributed to the similar microstructure, which was caused by the medium number of Fe-rich phase particles.

Copper powder was cryomilled for 12 hours to achieve particle size in the range of 2 μm to 25 μm, which powder was subsequently used as feedstock for the deposition of nanocrystalline (nc) Cu coating via cold spraying. The as-milled copper powder was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The particle size of the cryomilled Cu powder was detected by laser scattering. The microstructure of the coating was analyzed using SEM and scanning transmission electron microscopy (STEM). The XRD and HRTEM analysis showed that the grain size of the cryomilled Cu powder was about 5 to 40 nm. This nanoscale structure was retained after the cold spraying. The nanoindentation analysis showed that the nc Cu coating hardness value reached 3.3 GPa, which was higher than that of its coarse grained counterpart.

Cold spray technology, originated from the Institute of Theoretical and Applied Mechanics Siberian branch of the Russian Academy of Sciences, is a rapidly emerging industrial coating technology. Cold sprayed particles with high-velocity impact onto a substrate so as to induce severe plastic deformation and then create a deposit. For its low temperature and high velocity compared with thermal spraying, the cold spraying process is increasingly used in the industries for protective coating. The deposition characteristics of the particles, coating formation and bonding mechanism of the cold spraying process are different from thermal spraying. Many theory investigations of the cold spraying process contribute to the development of the high performance coatings, which makes the cold spraying process as a popular research field. Presently, the deposition characteristics, bonding mechanism, process optimization as well as classical applications of the cold spraying technology in the past are reviewed, and the interesting points for the further development, optimization and applications of this technology are also recommended.

Effects of the particles induced by strain on dynamic recrystallization and microstructure of the AA7050 aluminum alloy were investigated during hot deformation using X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD). Experimental results showed that partial recrystallized grains containing little sub-structure were produced during the solution treatment. Numerous particles were successfully obtained by the strain-induced precipitation during first-pass deformation at 573 K. The deformation promoted spheroidization and refinement of the precipitate particles. Then these particles pinned dislocations and grain boundaries inhibiting dynamic recrystallization during second-pass high-temperature deformation at 673 K and low angle grain boundary fraction was increased significantly to 83.8%. Furthermore, the tensile test indicated that microstructure with numerous low angle boundaries (LAGBs) and 5 μm sub-grains had increased the strength and ductility of the AA7050 aluminum alloy.Highlights► Experimental two-pass deformation process is different from conventional rolling. ► Globular precipitates were accelerated to produce by first-pass deformation. ► Second-pass deformation produced low angle grain boundaries owing to precipitates. ► Microstructure with numerous sub-structures had increased strength and ductility.

In this work, a mixture of as-atomized and as-cryomilled powders instead of the pure as-cryomilled powder was used as feedstock to achieve high density nanocrystalline coatings by cold spraying. Cryomilled powder with nanocrystalline grains was produced by mechanical milling under liquid nitrogen and the grain size range was from 5 to 30 nm. A mixture of 30 wt.% as-atomized powder and 70 wt.% as-cryomilled powder was sprayed onto the aluminum substrates. High density coatings were attained by use of this kind of mixture, which was described as an effective method to decrease porosity in the cold-sprayed nanocrystalline coating. The functions of the as-atomized powder in the coating were discussed. The mechanical behavior of the powders and the coating were studied using nanoindentation technique.