Baohong Zhu’s research while affiliated with General Research Institute for Nonferrous Metals (GRINM) and other places

The aging behavior of Al-Cu-Mg-Ag alloys with high Cu/Mg was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) using synchrotron radiation. TEM study reveals that the major strengthening phases of the alloy after aging at 160 °C for 10 h are Ω and less θ′. SAXS study shows that the scattering patterns are composed of several concentric circles at the beginning of aging process, which is replaced by the butterfly-wings scattering patterns with the increase of aging time. The butterfly-wings scattering patterns are composed of several branches. The angles between the branches are roughly equal to that between the habit planes of precipitates. The evolution of Guinier radius with aging time indicates the good coarsening resistance of the precipitates. The evolution of integrated intensity is consistent with the classical two-step precipitation process.

Introduction Experimental Results and discussion Conclusions Acknowledgements

Introduction Experimental Procedures Results and Discussion Summary Acknowledgement

Influence of silicon (Si) addition on aging precipitation behavior of an Al-4Cu-1.3Mg alloy was investigated by hardness measurements and TEM analysis. The results indicated that each of the Si-containing alloys exhibits an enhanced age-hardening response, a cubic phase, previously designated σ phase, was obtained. The σ phase was showed to be a (semi-)coherent and coplanar phase with the Al matrix, i.e.,{100}σ//{100}Al and <100>σ//<100>Al. In addition, S’ phase was observed. Si addition played an important role on the formation of σ phase. σ phases were observed in the Si containing alloy for all the aging conditions studied but was absent in Si-free alloy. The content of Si significantly influenced the volume fraction of σ phase in the alloy. Prolongation of aging time will be conducive to precipitation of a greater number of σ phases.

The effects of Zn, Mg, Cu content on lattice constants of the supersaturated solid solution of Al-Zn, Al-Mg, Al-Cu based binary alloys and three selected 7B04, 7050, 7B85 alloys were investigated by using X-ray diffraction pattern technique, and the effect of lattice distortion on the stability of the solid solution was attempted to describe the mechanism of quench sensitivity in age hardened Al alloys. The results show that the Cu is most sensitive to the lattice distortion of Al matrix when it was added to Al alloy to form supersaturated solid solution. The effect sequence of alloying elements to lattice constant of the 7XXX series aluminum alloy solid solution was: Cu > Mg > Zn. Evidence has been presented for the obvious expansion behavior of Al lattice in the supersaturated 7B04,7050, and 7B85 alloy. The order of the lattice distortion of solid solution of was: 7B04 > 7050 > 7B85. Compared to the 7B04 and 7050 alloy, the main alloying elements seems to be most stable in the solid solution of 7B85 alloy, and this could be used to explain the lowest quench sensitivity of 7B85 alloy among three selected 7XXX series alloys in this study.

The effects of interrupted multi-step aging on the microstructure and properties of Al-Cu-Mg-Ag-Zr alloy were studied by tensile, hardness, electrical conductivity tests and transmission electron microscopy (TEM). Interrupted multi-step aging delayed the peak aging time compared to one-step aging and kept the same levels of hardness, electrical conductivity, ultimate tensile strength (UTS), yield strength (YS) and elongation as those of the T6 temper alloy while increased the fracture toughness notably. Ω phase and a little θ′ phase precipitated and grew simultaneously in the process of one-step aging at 160°C. During the second-step aging at 65°C of interrupted multi-step aging, no TEM characteristic of Ω precipitates could be found. During the third step of interrupted multi-step aging, Ω began to dominate the microstructure like what happened in the process of one-step aging. The difference of properties between the T6 temper and the interrupted multi-step aged alloys might be related to the different precipitation sequences in the process of the two heat treatment technologies. Keywordsaluminum copper alloys–heat treatment–microstructure–fracture toughness–aging

A novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy was subjected to the retrogression and re-ageing (RRA) treatments at a lower range of retrogression temperatures from 170 to 200°C. The effect of RRA on the mechanical properties, electrical conductivity and the microstructure of the alloy has been investigated. The results indicate that an increase in the yield strength of the alloy can be achieved after RRA treatment. With increase of the retrogression temperature, the retrogression time for keeping the strength levels similar to T6 temper decreases rapidly. When submitted to RRA at 170°C for 90-120 min, the alloy can obtain a good performance on both SCC and mechanical strength; the electrical conductivity was above 40%IACS, reaching values typical for T76 condition and the tensile yield strength values were 552-570 MPa which is higher than that of the T6 temper. The microstructure is a very fine distribution of GP zones and η′ precipitates inside grains, similar to T6 condition and η precipitates on grain boundaries distributed similarly to T7 temper.

The effect of one-step aging temper on the mechanical properties, electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated. The results indicated that with elevating the aging temperature from 100°C to 160°C, the aging response rate was greatly accelerated, and the UTS at peak aging condition decreased, while the corresponding TYS increased. However, the electrical conductivity of the alloy became higher. After aging for 24 h at 120°C, the peak UTS and TYS values were achieved as 591 MPa and 541 MPa, respectively; but the alloy achieved a lower conductivity, 20.4 MS/m. When T6 temper was performed at 140°C for 14 h, the UTS decreased only by 1% of the former, whereas the TYS and the electrical conductivity increased obviously, which were up to 559 MPa and 22.6 MS/m, respectively. The major strengthening precipitates of the peak-aged alloy were GP zones and η′ phase. The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature. There were obvious PFZs along the grain boundary both in T6 conditions aged at 140°C and 160°C.

The 7B04 Al alloy is a precipitation hardenable, plate and forging material, which is widely used in China for strength critical aerospace structural applications. In this paper, fracture toughness, electrical conductivity and tensile properties of the alloy were investigated, and their dependence on ageing treatment details was described. Varying the heat treatment details strongly influences the microstructure and properties of the alloy. The alloy is identified to respond well to retrogression and reageing (RRA) temper. The retrogressing treated material at 180擄C for 1h and then reageing for 22h at 120擄C can achieve tensile properties comparable to a T6 condition as well as excellent conductivity. The high strength associated with optimized RRA conditions tend to result in relatively low levels of fracture toughness, but still slightly higher than T651 condition treated material. A correlation has been made among such properties, microstructure and fracture behavior, as characterized using TEM and SEM observations, and the results are discussed in the light of this relationship.

In this study, Si–30Al alloy was synthesized by the spray atomization and deposition technique. The microstructure and properties of the alloy were studied using optical microscopy, scanning electron microscopy, coefficient of thermal expansion (CTE) and thermal conductivity (TC) measurements, and 3-point bending tests. It was found that the microstructure of the alloy after hot pressing is composed of a continuous network of globular primary Si and interpenetrating secondary Al-rich phase. The property measurements results indicate that the spray-deposited 70Si30Al alloy has advantageous physical and mechanical characteristics, including low coefficient of thermal expansion (6.8 × 10− 6/K), high thermal conductivity (118 W/mK), low density (2.42 g cm− 3), high ultimate flexural strength (180 MPa) and Brinell hardness (261).