A Model of Dynamic Recrystallization in Alloys during High Strain Plastic Deformation

Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization

Investigations of a nanostructured FeMnSi shape memory alloy produced via severe plastic deformation

Low-cost iron-based shape memory alloys（SMAs） show great potential for engineering applications. The developments of new processing techniques have recently enabled the production of nanocrystalline materials with improved properties. These developments have opened avenues for newer applications for SMAs. The influence of severe plastic deformation induced by the high-speed high-pressure torsion（HSHPT） process on the microstructural evolution of an Fe–Mn–Si–Cr alloy was investigated. Transmission electron microscopic analysis of the alloy revealed the existence of nanoscale grains with an abundance of stacking faults. The high density of dislocations characteristic of severe plastic deformation was not observed in this alloy. X-ray diffraction studies revealed the presence of ε-martensite with an HCP crystal structure and γ-phase with an FCC structure.

High-efficiency ultrasonic assisted drilling of CFRP/Ti stacks under non-separation type and dry conditions

In this study,to address the low efficiency for conventional ultrasonic-assisted drlling(UAD)of carbon fiber-reinforced plastic and titanium alloy(CFRP/Ti)stacks,feasibility experiments of non-separation UAD,in which continuous cutting between the tool and the workpiece occurs at a high feed rate,are carried out.The experimental results indicate that,compared to conventional separation UAD,the non-separation UAD effectively reduces the cutting forces by 24.2%and 1.9%for CFRP stage and 22.1%and 2.6%for the Ti stage at the feed rates of 50 and 70μm/r,respectively.Furthermore,the non-separation UAD significantly improves hole quality,including higher hole diameter accuracy,lower hole surface roughness,and less hole damage.In addition,the non-separation UAD can decrease adhesive tool wear.This study demonstrates that,compared to conventional drilling(CD),the non-separation UAD can effectively improve drilling quality and tool life while maintaining high efficiency.

What is going on in magnesium alloys？

China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium （Mg） and its alloys in the world from a solid base laid by its prominent metallurgist and materials scientists over the past decades. Nowadays, a large number of young-generation researchers have been inspired by their predecessors and become the key participants in the fields of Mg alloys, which consequently led to the establishment of China Youth Scholar Society for Magnesium Alloys Research in 2015. Since then, the first two China Youth Scholars Symposiums on Mg Alloys Research had been held at Harbin （2015） and Chongqing （2016） China, respectively. A number of crucial research inter- ests related to fundamental and applied Mg research were discussed at the conferences and summarized in this short perspective, aiming to boost far-reaching initiatives for development of new Mg-based materials to satisfy the requirements for a broad range of industrial employments. Herein, four main aspects are included as follows： i） Plastic deformation mechanism and strengthening strategy, ii） Design and development of new Mg-based materials, iii） Key service properties, and iv） New processing technologies.

Dynamic deformation behavior of a face-centered cubic FeCoNiCrMn high-entropy alloy

In this study, mechanical tests were conducted oil a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates （10^-4-10^4 s^-1） to systematically investigate its dynamic response and underlying deformation mechanism. Materials with different grain sizes were tested to understand the effect of grain size, thus grain boundary volume, on the mechanical prop-erties. Microstructures of various samples both before and after deformation were examined using elec-tron backscatter diffraction and transmission electron microscopy. The dislocation structure as well as deformation-induced twins were analyzed and correlated with the measured mechanical properties. Plastic stability during tension of the current high-entropy alloy （HEA）, in particular, at dynamic strain rates, was discussed in lights of strain-rate sensitivity and work hardening rate. It was found that, under dynamic conditions, the strength and uniform ductility increased simultaneously as a result of the mas-sive formation of deformation twins. Specifically, an ultimate tensile strength of 734 MPa and uniform elongation of-63% are obtained at 2.3×10^3 s^-1, indicating that the alloy has great potential for energy absorption upon impact loading.

Effect of rolling deformation on microstructure and texture of spray-deposited magnesium alloy containing Mg-Nd-Zn typed LPSO

Billets of Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy were produced by spray-deposition（the Osprey process）.Effect of rolling deformation（T = 350？C, ε = 5%, 10%, and 15%, respectively） on microstructure and texture evolution of the Mg-9Al-3Zn-1Mn-6Ca-2Nd alloy was investigated by scanning electron microscopy（SEM）, transmission electron microscopy（TEM） and X-ray diffraction（XRD）. Results show that at pass reduction of ε = 5%, 10% and 15% at 350？C respectively, Mg-Nd-Zn typed 24R-LPSO structure was formed in（Ca, Nd）Al2phase（C15 Laves phase）. With the increase in pass reduction（i.e. 5%, 10% and 15%）, the texture pole density level of basal texture（0002） changed little and pyramidal texture（10 1ˉ3） were increased.In contrast, those of prismatic texture {101ˉ0} 〈11 2ˉ0〉 were increased initially and followed by a reduction, indicating texture randomization in the grain-refined Mg alloy. The combined contribution of LPSO phase and C15 phase was key to randomize the texture of the grain-refined Mg alloy. It was noted that the microcosmic plastic deformation of LPSO phase and nanometer-sized dispersed C15 phase impeded dislocation movement, led to dislocation tangles, and facilitated recrystallization.

Microstructural characteristics and deformation of magnesium alloy AZ31 produced by continuous variable cross-section direct extrusion

Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.

Tailoring Microstructure and Tribological Properties of Cold Deformed TiZrAlV Alloy by Thermal Treatment

Microstructure evolution and tribological properties of a new Ti Zr Al V alloy have been investigated in the present study. Various microstructures, i.e., equiaxed grain structure, dual-phase lamella structure, and heterogeneous lamellar structure, have been successfully prepared, and the effect of the microstructure on tribological properties was explored by means of cold severe plastic deformation combined with subsequent recrystallization annealing and aging treatments. The special heterogeneous lamellar-structured alloy exhibits a high ultimate tensile strength（~1545 MPa）,reasonable ductility（~7.9%）, and excellent wear resistance as compared with the equiaxed grain-structured and dualphase lamella-structured alloy. The present study demonstrates an alternative route for enhancing the tribological properties of alloys with heterogeneous lamellar structure.

Developments of New Sheet Metal Forming Technology and Theory in China

Developments of new sheet metal forming technology and theory in China are reviewed in detail in this paper.Advances of crystal plasticity on the deformation mechanism of Mg alloy are firstly described, especially its applications on the prediction of sheet forming process. Then, a new macroscopic constitutive model is introduced, which possesses an enhanced description capacity of tension/compression anisotropy and anisotropic hardening. In order to take into account the twinning process of hexagonal close-packed material, a modified hierarchical multi-scale model is also established with adequate accuracy in a shorter computational time. The advanced forming limit of sheet metal, mainly about aluminum alloy, is also investigated. Besides the above theory developments, some new sheet metal forming technologies are reviewed simultaneously. The warm forming technology of Mg alloy is discussed. New processes to form sheet parts and to bend tubes are proposed by using hard granules. On the other hand, a new kind of ultra-high-strength steel based on typical22 Mn B5 by introducing more residual austenite and Cu-rich phase to increase the elongation and strength and its novel forming method that integrates hot stamping and quenching participation are proposed. Progresses in sheet hydroforming,press forging and electromagnetic forming of sheet metal parts are also summarized.

Mechanical Properties and Microstructure Evolution of AA1100 Aluminum Sheet Processed by Accumulative Press Bonding Process

Accumulative press bonding（APB） is a novel variant of severe plastic deformation processes,which is devised to produce materials with ultra-fine grain.In the present work,the mechanical properties and microstructural evolution of AA1100 alloy,which is produced by APB technique,were investigated.The study of the microstructure of AA1100 alloy was performed by optical microscopy.The results revealed that the grain size of the samples decreased to 950 nm after six passes of APB process.The yield strength of AA1100 alloy after six passes of the process increased up to 264 MPa,which is three times higher than that of the as-cast material（89 MPa）.After six passes,microhardness values of AA1100 alloy increased from 38 to 61 HV.Furthermore,the results showed that the behavior of variations in mechanical properties is in accordance with the microstructural changes and it can be justified by using the Hall-Patch equation.Moreover,the rise in the yield strength can be attributed to the reduction in the grain size leading to the strain hardening.

Serration and Noise Behavior in Advanced Materials

The Chinese Materials Research Society（C-MRS）Conference（2015）was held in the Guizhou Park Hotel International Conference Center,Guiyang,China,from July 10-14,2015.This conference consists of 30symposia,including 4international symposia.As one of 4international symposia,＂Serration and noise behavior in advanced materials＂