Recent advances in ageing of 7xxx series aluminum alloys: A physical metallurgy perspective

Dr. Suib is a Board of Trustees Distinguished Professor of Chemistry and received the CT Medal of Science for his work in catalysis, semiconductors and ceramic composites. He received a B. S. degree in chemistry and geology at the State University College of New York at Fredonia. His graduate and postdoctoral training was completed at the University of Illinois at Champaign Urbana. In 1980, Steve joined UConn’s faculty in the Department of Chemistry and served as the head of the department for 10 years. He is a Fellow of the American Chemical Society and the American Institute of Chemists.

Materials by Design

Wire arc additive manufacturing (WAAM) is a promising approach to producing large-scale metal structures. The investigation on the WAAM of aluminum alloys has lasted for over 17 years and covered multiple alloy systems. However, fundamental research on the WAAM of quaternary Al-Zn-Mg-Cu alloys is still lacking. This study focuses on understanding the microstructural characteristics and mechanical properties of an ultra-high-strength Al-Zn-Mg-Cu alloy fabricated by WAAM. A single-pass multilayer component is successfully fabricated. Results indicate that a single deposition layer consists of two types of columnar grains with different textures and origins. Nanoscale second phases are observed to precipitate during the manufacturing process with location-dependent sizes and volume fractions due to different thermal histories. The microhardness of the cross-section exhibits a special un-uniform distribution between 75–164 HV0.2 from the substrate to the top of the component. The WAAM deposited component shows higher overall tensile properties than the as-fabricated spray formed counterpart. The average yield strength and ultimate strength are higher in the vertical direction than in the horizontal direction, while the difference in elongation is small.

Wire arc additive manufacturing of Al-Zn-Mg-Cu alloy: Microstructures and mechanical properties

The 2195 aluminum alloy has been widely utilized in the aerospace field, of which dynamic recrystallization microstructures have a substantial effect on the mechanical properties of aerospace parts. In this study, 2195 aluminum alloy was compressed at 300–520 °C using a Gleeble 3500-GTC thermo-mechanical testing system. The discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) behavior of 2195 aluminum alloy at medium/high temperature was studied. The results demonstrated that during medium temperatures (300–360 °C) deformation the main softening mechanism was DDRX, and at high temperatures (420–520 °C), it was CDRX. CDRX of 2195 aluminum alloy involved three types of subgrain-forming mechanisms: dislocation tangling to form subgrains, microscopic shear bands to form subgrains, and the coalescence of two small subgrains to form larger subgrains. In addition, several recrystallized grains underwent geometric dynamic recrystallization (GDRX) at high temperature and extensive deformation (480 °C-80% or 520 °C-60%).

Dynamic recrystallization mechanisms of 2195 aluminum alloy during medium/high temperature compression deformation

Grain refinement and weak-textured structures based on the dynamic recrystallization of Mg–9.80Gd–3.78Y–1.12Sm–0.48Zr alloy

A high Zn-containing Al-Zn-Mg-Cu alloy was researched due to excellent overall performances. The hardness, electrical conductivity and mechanical properties were investigated and detailed aging parameters subjected to T6, T79, T74 and T73 were proposed. The matrix precipitates of various aging tempers were investigated by transmission electron microscope (TEM) and high-resolution transmission electron microscope (HREM) techniques and quantitative information of matrix precipitates was extracted from the bright-field TEM images projected along 〈110〉Al orientation with the aid of an imaging analysis. The fatigue crack propagation (FCP) behaviors subjected to different aging tempers were investigated, the related fracture morphology of the stable expanding regions was analyzed and corresponding fatigue striations were measured to verify the FCP rates. The results showed that with the deepening of aging degree, the matrix precipitates coarsened with an expanding of precipitate size distribution and an enlargement of average precipitate size while the precipitates evolved from GP zones and η' phase to η' phase and η phase. The FCP resistance was improved with the aging degree deepens and the evolution of related tearing ridge, tearing dimple and fatigue striation also proved it. Due to a smaller cyclic plastic zone of the alloy with various tempers compared with the average grain size, the FCP rate was significantly influenced by matrix precipitate characteristics and a theoretical model which directly correlated FCP rate with matrix precipitate characteristics was proposed. From T6 state to T73 state, the enlargement of cuttable GP zones and η' phase, its evolution to η phase and the nucleation, growth and coarsening of η phase were in favor of enhancing the FCP resistance.

Over-aging influenced matrix precipitate characteristics improve fatigue crack propagation in a high Zn-containing Al-Zn-Mg-Cu alloy

Effects of Zn addition on the age hardening behavior and precipitation evolution of an Al-Mg-Si-Cu alloy

Natural aging behavior in pre-aged Al–Mg–Si–Cu alloys with and without Zn addition

In the present work, the influence of various retrogression treatments on hardness, electrical conductivity and mechanical properties of a high Zn-containing Al–Zn–Mg–Cu alloy is investigated and several retrogression regimes subjected to a same strength level are proposed. The precipitates are qualitatively investigated by means of transmission electron microscopy (TEM) and high-resolution transmission electron microscopy techniques. Based on the matrix precipitate observations, the distributions of precipitate size and nearest inter-precipitate distance are extracted from bright-field TEM images projected along 〈110〉Al orientation with the aid of an imaging analysis and an arithmetic method. The results show that GP zones and η′ precipitates are the major precipitates and the precipitate size and its distribution range continuously enlarge with the retrogression regime expands to an extent of high temperature. The nearest inter-precipitate distance ranges obtained are quite the same and the average distance of nearest inter-precipitates show a slight increase. The influence of precipitates on mechanical properties is discussed through the interaction relationship between precipitates and dislocations.

Huang Shuhui

Papers

Over-aging influenced matrix precipitate characteristics improve fatigue crack propagation in a high Zn-containing Al-Zn-Mg-Cu alloy

Effects of Zn addition on the age hardening behavior and precipitation evolution of an Al-Mg-Si-Cu alloy

Natural aging behavior in pre-aged Al–Mg–Si–Cu alloys with and without Zn addition

Effect of Various Retrogression Regimes on Aging Behavior and Precipitates Characterization of a High Zn-Containing Al–Zn–Mg–Cu Alloy

Pre-aging on early-age behavior and bake hardening response of an Al-0.90Mg-0.80Si-0.64Zn-0.23Cu alloy