Optimizing the strength and ductility of fine structured 2024 Al alloy by nano-precipitation

Alloys with grain or subgrain structures refined down to 1 μm or below usually have high strength, but often inadequate tensile ductility. Past efforts in improving their ductility have usually led to a sacrifice of strength. We have developed an effective approach in achieving both high strength and high ductility in a 2024 Al alloy. The approach involves solution-treatment to partially dissolve T-phase particles, cryo-rolling to produce a fine-structure containing a high density of dislocations and submicrometer subgrains and aging to generate highly dispersed nano-precipitates. It was found that the remnant T-phase particles made it very effective in accumulating dislocations during cryo-rolling, which in turn promoted the precipitation of nanosized S′ precipitates with an interparticle spacing of only 10–20 nm. Such a high density of S′ precipitates enabled effective dislocation pinning and accumulation, leading to simultaneous increases in strength, work-hardening ability and ductility.     

Short-circuit diffusion in an ultrafine-grained copper–zirconium alloy produced by equal channel angular pressing

Many unusual properties of ultrafine grain materials obtained by equal channel angular pressing (ECAP) are commonly attributed to non-equilibrium grain boundaries. Such grain boundaries are expected to exhibit higher values of energy, higher amplitude of strain fields, a larger free volume and a higher diffusivity than their relaxed counterparts. In the present study, the diffusivity of ⁶³Ni radiotracer in ECAP-processed Cu–0.17 wt.% Zr alloy was measured in the low-temperature range of 150–350 °C under conditions at which no bulk diffusion occurs. The microstructure observations after annealing indicate that alloying with Zr is essential for stabilizing the ECAP-processed alloys against grain growth and recrystallization. In all samples studied the experimentally measured diffusion profiles exhibited two distinct slopes, which are associated with “slow” and “fast” short-circuit diffusion paths. The diffusivity of “slow” diffusion paths in the ECAP-processed samples coincides with the diffusivity via relaxed grain boundaries in the coarse grain Cu measured by the same radiotracer method at similar temperatures. We associate the “fast” diffusion paths observed in this study with the non-equilibrium grain boundaries produced by ECAP.     

Microstructure evolution and deformation behavior of ultrafine-grained Al–Zn–Mg alloys with fine η′ precipitates

An aged Al–5Zn–1.6Mg alloy with fine η′ precipitates was grain refined to ～100 nm grain size by means of confined channel die pressing. Microstructure observations and mechanical tests were carried out to characterize the materials before and after various degrees of severe plastic deformation. Deformation processing enhanced the strength of the alloy, but limited its work hardenability. An analysis of deformation mechanisms revealed that plasticity proceeded by dislocation slip through ultrafine-grained cellular and subgrain arrangements. η′ precipitates strengthened the alloy by dispersion hardening, but retarded an increase in the strain rate sensitivity during grain refinement. The influence of η′ precipitates is discussed with respect to their effect on dislocation configurations and deformation mechanisms during processing of the alloy.     

ECAP法制备超细晶铝合金材料的超塑性行为

研究经多道次等径弯曲通道变形后Al-3%Mg-0.5%Zr铝合金的超塑性行为.研究表明:晶粒尺寸由变形前的50 μm经过8道次等径弯曲通道变形后细化为0.3μm;随后,在330℃退火保温1 h的条件下,其晶粒尺寸长大至10 μm;在500℃、应变速率1×10-3s-1的拉伸实验中,该超细晶材料的最大延伸率高达370%,呈现出良好的超塑性.     

Static mechanical properties and ductility of biomedical ultrafine-grained commercially pure titanium produced by ECAP process

Equal channel angular pressing (ECAP) is one of the most effective processes to produce ultra-fine grain (UFG) and nanocrystalline (NC) materials. Because the commercially pure titanium exhibits excellent biocompatibility properties, it has a significant potential to be utilized as an implant material. The low static and dynamic strengths of the pure titanium are one of the weaknesses of this material. This defect can be removed by applying the ECAP process on the pure titanium. In this work, the commercially pure titanium Grade 2 (CP-Ti of Grade 2) was pressed at room temperature by the ECAP process via a channel angle of 135° for 3 passes. The microstructural analysis and mechanical tests such as tensile test, hardness test, three-point bending test and Charpy impact test were all carried out on the ECAPed CP-Ti through 3 passes. The microstructural evolution reveals that by applying the ECAP process, coarse grain (CG) structure develops to UFG/NC structure. Moreover, the results of the mechanical tests show that the process significantly increases the yield and ultimate tensile strengths, bending strength, hardness and fracture toughness of the commercially pure titanium so that it can be used as a replacement for metallic alloys used as biomaterials.     

The influence of the ultrafine-grained structure on passivation of copper

The influence of ultrafine-grained structure on passivation of copper in borate solutions was studied. Ultrafine-grained cooper was prepared by the equal channel angular extrusion. It was shown that, under the conditions of anodic oxidation, an oxide film with improved protective properties is formed on the ultrafine-grained sample. This film is characterized by a small thickness, low roughness, and high content of copper(I) oxide.     

CuCrZr合金中沉淀相的控制

通过SEM和力学性能试验,研究了不同热处理工艺下CuCrZr合金沉淀相尺寸和分布对合金力学性能的影响。结果表明,经固溶退火+淬火+时效处理后,热锻态CuCrZr合金中的沉淀相尺寸和分布存在“遗传”特性,高冷却速率有益于阻碍沉淀相的聚集和粗化;时效处理前增加冷加工工艺有利于获得均匀且细小的沉淀相,从而获得优异且稳定的力学性能。     

Increasing the strength and ductility of weldments in austenitic steels

Conclustions The same strength and ductility of the weld seam and the base metal in austenitic steels subjected to cold deformation are ensured by preliminary deformation of the seam metal (=6–8%) and hardening.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 45–47, April, 1982.     

Tailoring strength and ductility of high-entropy CrMnFeCoNi alloy by adding Al

High-entropy alloys with high strength and acceptable ductility at both room and elevated temperatures for high-temperature structural applications are desired....