Haichun Jiang

Bio: Haichun Jiang is an academic researcher from Central South University. The author has contributed to research in topics: Microstructure & Alloy. The author has an hindex of 6, co-authored 8 publications receiving 73 citations. Previous affiliations of Haichun Jiang include RWTH Aachen University.

Hot tensile deformation behaviors and a phenomenological AA5083 aluminum alloy fracture damage model

Abstract: In this study, the tensile deformation of the AA5083 aluminum alloy at elevated temperatures was elucidated via thermo–mechanical tests conducted at various temperatures (553–793 K) and strain rates (0.01–10 s−1). Furthermore, the effects of the deformation parameter on the flow stress, microstructure evolution, fracture characteristics, and underlying mechanisms were discussed, and a new phenomenological fracture damage model was proposed to predicate the fracture strain. The results were as follows. Increasing the temperature or decreasing the strain rate reduced the flow stress, increased the elongation, and accentuated the intergranular fracture characteristic of the alloy. Under the tested conditions, dislocation movement and ductile fracture were observed to be the primary deformation mechanism and fracture mechanism, respectively. Dynamic recrystallization was enhanced by increasing the temperature or the strain rate. Under the smallest strain rate (0.01 s−1), the elongation of the material drastically decreased at a deformation temperature of 793 K owing to grain-boundary weakening. The fracture damage predicted using the fracture damage model agreed well with the experimental results, with a maximum relative error of only 5.23%.

Dynamic properties evaluation of 2519A aluminum alloy processed by interrupted aging

Abstract: Dynamic properties of 2519A aluminum alloy processed by interrupted aging are assessed in this work At strain rate of 6900 s−1, the dynamic yield strength and absorption energy of this material are up to 6909 MPa and 3355 MJ/m3, respectively Denser and finer θ′ precipitates contribute to these enhancements

Intermetallic phase evolution of 5059 aluminum alloy during homogenization

Abstract: Intermetallic phase evolution of 5059 aluminum alloy during homogenization was investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD). The results show that severe dendritic segregation exists in as-cast alloy. The dissolvable intermetallic phases in as-cast alloy consist of Zn- and Cu-rich non-equilibrium β (Al3Mg2) phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si phase. During the homogenization, Zn- and Cu-rich non-equilibrium β (Al3Mg2) phase, Fe-rich eutectic Al6Mn phase and equilibrium Mg2Si gradually dissolve into matrix. Fine dispersed β(Al3Mg2) particles and rod-shaped Al6Mn particles form in the Al matrix after homogenization. The proper homogenization processing is at 450 °C for 24 h, which is consistent with the results of homogenizing kinetic analysis.

Grain structure and microtexture evolution during superplastic deformation of 5A90 Al-Li alloy

Abstract: The microstructural evolution of banded 5A90 Al-Li alloy during superplastic deformation at 475 °C with an initial strain rate of 8×10−4 s−1 was studied using EBSD technique. The results showed that, before deformation, the grain shape appeared to be banded, the most grain boundaries belonged to low-angle boundaries, and the initial sheet had a dominate of {110}«112» brasstexture. During deformation, there were grain growth, grain shape change, misorientation increasing and textural weakening. The fraction of high-angle boundaries increased rapidly once the flow stress reached the peak value. Corresponding deformation mechanism for various stages of deformation was suggested. Dislocation activity was the dominant mechanism in the first stage, then dynamic recrystallization occurred, and grain rotation was expected as an accommodation for grain boundary sliding (GBS). At large strains, GBS was the main mechanism.

Influence of Ce addition on impact properties and microstructures of 2519A aluminum alloy

Abstract: Dynamic impact testing of 2519A aluminum alloy with additions of 0, 0.2 and 0.4 wt% Ce was carried out by a split Hopkinson pressure bar (SHPB) equipment performed at temperatures (293 K and 573 K) and different nominal strain rates (1200, 3100 and 5100 s−1). The influences of Ce contents on impact mechanical properties and microstructures of 2519A aluminum alloy were investigated. The results show that the addition of 0.2 wt% Ce leads to an increased precipitation phase volume fraction, as well as a more dispersive and homogeneous distribution of θ′ precipitates, which improves the ability of absorbing impact energy. Adiabatic shear lines, fibrous structure and dynamic recrystallizied grains were observed in the impacted specimens and could be attributed to stress concentration and adiabatic temperature rise.

Control of second-phase particles in the Al-Mg-Mn alloy AA 5083

Abstract: The purpose of the present work is to understand the evolution of microstructure and microchemistry during homogenization of the Al-Mg-Mn alloy AA 5083 (Al Mg4.5 Mn0.7) and its influence on down-stream materials properties. The evolution of the particle state during solidification and subsequent homogenization annealing was tracked with a variety of experimental characterization methods and simulated with microchemistry models to analyse the changes in solute level and precipitation. Different homogenization practices were characterized by different sizes, volumes and densities of dispersoids which, in turn, had a clear impact on materials properties, including recrystallization behaviour and flow stress.

Ultrasonic spot welding of carbon fiber reinforced epoxy composites to aluminum: mechanical and electrochemical characterization

Abstract: The mechanical and electrochemical behavior of ultrasonic spot welded hybrid joints, made of AA5754 aluminum and carbon fiber reinforced epoxy with a co-cured thermoplastic surface layer, was studied. The effect of the welding parameters (energy and force) and the thickness of a thermoplastic film, applied as an upper ply in the composite lay-up, on the development of adhesion strength, was investigated. The best mechanical results were obtained when the welding parameters were able to achieve a large bonding area of mechanical interlocking between naked carbon fibers and aluminum and a better load distribution. The electrochemical results excluded the possibility of galvanic corrosion between aluminum and composite adherends thanks to the insulating action provided by the thermoplastic film.

Effects of strain rate on dynamic mechanical behavior and microstructure evolution of 5A02-O aluminum alloy

Abstract: This paper studies the effects of strain rate on dynamic mechanical behavior and microstructure evolution of 5A02-O aluminum alloy at room temperature. Based on the results of the dynamic tensile tests and compressive tests at strain rates of 1000–5000 s −1 by split Hopkinson bar as well as the results of quasi-static tests at strain rate of 0.001 s −1 , it is shown that with increasing strain rate, the flow stress and tensile strength significantly increase and notable strain hardening and thermal softening behaviors are observed for 5A02-O with elongation of 63.00% and softening ratio of 73.23% at the strain rate of 4000 s −1 . The strain rate sensitivity for 5A02-O is enhanced in the range of 1000–3000 s −1 . Scanning electron microscopy (SEM) observations illustrate that the fracture surfaces are characterized by larger and deeper dimple-like structure with more precipitates at higher strain rates, which indicates the ductile failure mode. The enhancement of ductility is interpreted via the inertia effect which may contribute to diffuse necking, slow down the necking development and delay the onset of fracture. Furthermore, transmission electron microscopy (TEM) observations show that higher strain rate leads to higher dislocation density, smaller cell size with thinner cell wall and the appearance of dislocation wall with parallel dislocation lines. Dislocation cells are incomplete under dynamic deformation. In addition, the micro-hardness of 5A02-O increases with increasing strain rate.

Aging behavior of an Al–Cu–Mg alloy

Abstract: Effect of aging temperature on precipitation behavior and mechanical properties of an AA2519 alloy was examined. Long-term natural aging provides the best combination of strength and ductility by the precipitation of dense Guinier–Preston and Guinier–Preston–Bagaryatsky zones. This phenomenon, called “delayed hardening”, has the same origin as the “rapid hardening” in AA2X24 alloys subjected to artificial aging. At 190 °C, high density of θ″-phase provides high strength. Peak aging is characterized by insignificant increase in strength associated with additional precipitation of θ′-phase. The overaging leads to the formation of precipitate structure dominated by θ′-phase. The formation of θ″- and θ′-phases can consume ∼0.7 and ∼3.3%Cu, respectively. Despite this, the number density of θ″-phase precipitates is higher than that of θ′-phase ones by a factor of ∼40. The θ″-phase is effective strengthening agent in the AA2519 alloy. The Ω-phase plates with a very high aspect ratio (AR) > 100 precipitate during artificial aging.

Mechanical properties and corrosion resistance of Al–Cu–Mg–Ag heat-resistant alloy modified by interrupted aging

Abstract: The effects of interrupted aging on the microstructure, mechanical properties and corrosion resistance of Al–Cu–Mg–Ag heat-resistant alloy were investigated by hardness tests, tensile tests, exfoliation corrosion (EXCO) tests, transmission electron microscopy (TEM) and electrochemical analysis. Results showed some phases precipitated during the interrupted aging process in Al–Cu–Mg–Ag alloy, which were called secondary precipitations. The precipitations both in the grains and the grain boundaries were refined by interrupted aging. The phases on the grain boundaries of the single-aged sample were distributed discontinuously, whereas those of the interrupted-aged sample were chain-like with a wider precipitation free zone (PFZ) on both sides of the grain boundary. The elongation of Al–Cu–Mg–Ag alloy increased by 37.7% while the tensile and yield strength slightly decreased after interrupted aging. The corrosion resistance of Al–Cu–Mg–Ag alloy was mainly determined by the PFZ with the lowest self-corrosion potential. The coarse and discontinuously distributed precipitations on the grain boundaries of the single-aged sample gave rise to larger efficient PFZ width than that of the interrupted-aged sample, which then lead to wider corrosion passageway and resulted in the better exfoliation corrosion resistance of Al–Cu–Mg–Ag alloy treated by interrupted aging.