Effect of cryogenic rolling and annealing on the microstructure evolution and mechanical properties of 304 stainless steel

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.

Comparisons of interface microstructure and mechanical behavior between Ti/Al and Ti-6Al-4V/Al bimetallic composites

The microstructure, interface thickness, element distribution and interfacial mechanical behavior of Ti-6Al-4V/Al couples prepared by an insert moulding method were investigated in depth in this paper. Moreover, Ti/Al bonding was also given as a comparison for understanding the interface bonding mechanism. It is shown that there is much thinner compact sub-layer for the interface of the Ti-6Al-4V/Al joint, whose morphology is obviously different from that of the Ti/Al joint. The Ti-6Al-4V/Al interface has been proven to contain a slight content of vanadium. Moreover, both the shear strength and the interface reaction rate of Ti-6Al-4V/Al compound materials are lower than those of the Ti/Al ones.

Effect of alloying elements and processing parameters on the Portevin–Le Chatelier effect of Al–Mg alloys

The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of A1-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testing was performed in various Zn and Mg contents under different annealing and cold-rolling conditions. In the results, the stress drop and reloading time of serrations increase with increasing plastic strain and exhibit a common linear relationship. The increase rates of stress drop and reloading time increase with increasing Mg or Zn content. The alloys with a greater intensity of serrated yielding generally exhibit a greater elongation. The stress drop and reloading time of serrations decrease with increasing grain size in the case of the annealed samples. The cold-rolled sample exhibits the most severe serra- tion because it initially contains a large number of grain boundaries and dislocations.

Interfacial microstructure and mechanical properties of Ti-6Al-4V/Al7050 joints fabricated using the insert molding method

Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 μm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl_3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl_3 and TiAl_3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.

Effect of rolling geometry on the mechanical properties, microstructure and recrystallization texture of Al–Mg–Si alloys

The effect of rolling geometry on mechanical properties, microstructure, and recrystallization texture of Al-Mg-Si alloys was studied by means of tensile tests, microstrucmral observations, and electron backscatter diffraction measurements. The results reveal that the elongation and the average plasticity strain ratio （r） values of the T4P （pre-aging plus natural aging）-treated alloy sheet with a rolling geome- try value between 1 and 3 are somewhat higher than those of the T4P-treated sheet with a rolling geometry value between 3 and 6. The deformation and recrystallization microstructures of the sheet with a rolling geometry value between 1 and 3 are more uniform than those of the sheet with a rolling geometry value between 3 and 6. The former also possesses somewhat higher surface quality. H {001 } 〈110〉 and Goss {110}〈001〉 orientations are the main recrystallization texture components for the former case, whereas the latter case only includes H {001 } 〈 110〉 orientation. Texture gradients are present in the two alloy sheets. Shear texture component F on the surface of the sheet with a rolling geometry value between 3 and 6 and its higher texture gradients have revealed that non-uniform deformation occurred during cold rolling. The effects of texture on the yield strength and r value were also discussed.

Effect of Ni addition on microstructure and mechanical properties of Al–Mg–Si–Cu–Zn alloys with a high Mg/Si ratio

The effect of adding 0.03wt%Ni on the microstructure and mechanical properties of Al–Mg–Si–Cu–Zn alloys was systematically studied.The results reveal that the number density of spherical Fe-rich phases within grains increases with the addition of Ni,accompanied by the formation of Q(Al3Mg9Si7Cu2)precipitates around the spherical Fe-rich phases.Additionally,Ni addition is beneficial to reducing the grain size in the as-cast state.During the homogenization process,Q phases could be completely dissolved and the grain size could remain basically unchanged.However,compared with the Ni-free alloy,the Fe-rich phase in the Ni-containing alloy is more likely to undergo the phase transformation and further form more spherical particles during homogenization treatment.After thermomechanical processing,the distribution of Fe-rich phases in the Ni-containing alloy was further greatly improved and directly resulted in a greater formability than that of the Ni-free alloy.Accordingly,a reasonable Ni addition positively affected the microstructure and formability of the alloys.

Effect of particle size distribution on the microstructure,texture,and mechanical properties of Al–Mg–Si–Cu alloy

The effect of particle size distribution on the microstructure,texture,and mechanical properties of Al–Mg–Si–Cu alloy was investigated on the basis of the mechanical properties,microstructure,and texture of the alloy.The results show that the particle size distribution influences the microstructure and the final mechanical properties but only slightly influences the recrystallization texture.After the pre-aging treatment and natural aging treatment(T4 P treatment),in contrast to the sheet with a uniform particle size distribution,the sheet with a bimodal particle size distribution of large constituent particles and small dispersoids exhibits higher strength and a somewhat lower plastic strain ratio(r) and strain hardening exponent(n).After solution treatment,the sheet with a bimodal particle size distribution of large constituent particles and small dispersoids possesses a finer and slightly elongated grain structure compared with the sheet with a uniform particle size distribution.Additionally,they possess almost identical weak recrystallization textures,and their textures are dominated by CubeND {001}<310> and P {011}<122> orientations.

Mechanical properties and constitutive behaviors of as-cast 7050 aluminum alloy from room temperature to above the solidus temperature

The mechanical properties and constitutive behaviors of as-cast AA7050 in both the solid and semi-solid states were determined using the on-cooling and in situ solidification approaches, respectively. The results show that the strength in the solid state tends to increase with decreasing temperature. The strain rate plays an important role in the stress–strain behaviors at higher temperatures, whereas the influence becomes less pronounced and irregular when the temperature is less than 250°C. The experimental data were fitted to the extended Ludwik equation, which is suitable to describe the mechanical behavior of the materials in the as-cast state. In the semi-solid state, both the strength and ductility of the alloy are high near the solidus temperature and decrease drastically with decreasing solid fraction. As the solid fraction is less than 0.97, the maximum strength only slightly decreases, whereas the post-peak ductility begins to increase. The experimental data were fitted to the modified creep law, which is used to describe the mechanical behavior of semi-solid materials, to determine the equivalent parameter fGBWL, i.e., the fraction of grain boundaries covered by liquid phase.

Microstructure and mechanical properties of cryorolled AZ31 magnesium alloy sheets with different initial textures

AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.

Microstructure characterization in a sensitized Al-Mg-Mn-Zn alloy

Alloying elements, present in the aluminum solid solution or the precipitates, influence the corrosion resistance of A1-Mg-Mn-Zn alloys. In this study, sensi- tizing treatment was applied to an A1-Mg-Mn-Zn alloy to modify the precipitation at the grain boundaries or in the grains. Transmission electron microscopy （TEM） and scanning electron microscope （SEM） were used to characterize various second-phase particles and determine their orientation relationship with the A1 matrix. After sensitizing treatment, z-phase （Mg32（Al, Zn）49） is observed to precipitate along the grain boundaries in a coarser size, producing a discontinuous grain boundary precipitate structure. In addition, Mn-rich particles are found to form with various shapes, such as global, plate and rhombus.

Twinning Behavior of a Basal Textured Commercially Pure Titanium Alloy TA2 at Ambient and Cryogenic Temperatures

Twinning greatly affects the microstructure and mechanical performance of titanium alloys.The twinning behavior of a basal textured commercially pure titanium TA2 plates rolled to 4% reduction at the ambient and cryogenic temperatures has been investigated.Microstructures of the rolled samples were investigated by optical microscope（OM）and the twinning analysis was carried out based on orientation data collected by electron back-scatter diffraction（EBSD）.{1122}contraction twins,{1124}contraction twins and {1012}extension twins have been observed.Twinning mode activity varied with rolling temperature.Twinning is considered as the dominant deformation mechanism during rolling at both temperatures for the strain condition.Larger proportion of grains activates twinning during cryorolling,and greater number and more diverse types of twins are observed;manifestly related to the suppression of dislocation slips at the cryogenic temperature.{1122}contraction twins are the dominate twin type within samples rolled at both temperatures.Several{1124}contraction twins are observed in the cryorolled sample while there are only a few in the sample rolled at room temperature.A few tiny{1012}twins have been identified in both samples.{1124}contraction twins are preferentially activated at cryogenic deformation temperature and the{1012}extension twins may result in local strain accommodation.