Yon Gan Zhang

Investigation of Quench Sensitivity of an Al-7.5Zn-1.7Mg-1.4Cu-0.12Zr Alloy

In the present work, quench sensitivity of an Al-7.5Zn-1.7Mg-1.4Cu-0.12Zr alloy is investigated by temperature-time-property (TTP) curve and TEM analysis, comparing with traditional AA 7B04 and AA 7150. The results indicate that the nose temperature of TTP curve and the corresponding incubation period of the alloy, AA 7150 and AA 7B04 are about 290°C/4.5s, 320°C/2.6s and 335°C/0.1s, respectively, The nose temperature of the alloy is the lowest among three alloys and the critical time at the nose temperature is the longest for the alloy, which is obvious that the alloy has lower quench sensitivity. Further TEM analysis shows that, with the prolongation of keeping time at the nose temperature, quench-induced precipitation phenomenon becomes obvious.

Effect of Temperature on Microstructure and Mechanical Properties of Spray Forming Al-8.5Fe-1.3V-1.7Si Alloys

Heat-resistant Al-8.5Fe-1.3V-1.7Si alloys were prepared by spray forming technique. The effect of temperature on microstructure and mechanical properties of the alloys was studied by optical microscope(OM), transmission electron microscope(TEM) with energy dispersive spectrometer(EDS), X-ray diffraction(XRD), differential scanning calorimeter(DSC) in this paper. The research results show that the microstructure of the material doesn’t change obviously after being hold for 3 hours at 420°C temperature. When the temperature is over 420°C, the second coarse phases are found in the alloy. The study on the microstructure of the alloy exposed at 400°C for 100 hours shows that the alloy has excellent high temperature stability. And the main second phase in the alloy is spherical a-Al12(Fe,V)3Si, with a little other phases such as Al13Fe4, Al6Fe, Al9FeSi3 and so on.

Quantitative Investigation on Nano-Scale Precipitates in an Al-7.5Zn-1.7Mg-1.4Cu-0.12Zr Alloy under Various Aging Tempers

In the present study, a systematic study of nanoscale precipitates in an Al-7.5Zn-1.7Mg-1.4Cu-0.12Zr alloy have been carried out for various typical aging tempers, including T6, T76, T74, T73 and RRA treatments, by combining synchrotron-based small-angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) techniques. Based on the TEM observations, quantitative and statistical structural information, including precipitate size, volume fraction, number density and inter-precipitate distance have been extracted from SAXS data through model fitting. The results show that the T6 peak-aged alloy with the smallest precipitate size has the highest number density and lowest volume fraction of precipitates. Under two-step T7X over-aged tempers, with the deepen of aging degree, the precipitate size, volume fraction and inter-precipitate distance increases, but the number density decreases. The size distribution of precipitates for the RRA-treated alloy is in between that of T6 and T76. The results also show that as the degree of over-aging deepens, the precipitate size distribution interval becomes broader.

Microstructure and Properties of an Al-7.5Zn-1.5Mg-1.4Cu-0.12Zr Alloy Forging

In this present work, the microstructure and properties of an Al-7.5Zn-1.5Mg-1.4Cu-0.12Zr alloy forging in T7452 condition has been investigated by means of OM, TEM and EBSD analysis and varied properties test. The results indicate that there are obvious differences in grain morphology, precipitation characteristics and recrystallization degree along the thickness direction of the forging. The strength of the alloy forging is stable and varies less than 10% along the thickness direction. The alloy forging in the T7452 condition shows high strength, high toughness and good corrosion resistance, with the UTS, TYS, elongation and electrical conductivity values being 500~530 MPa, 460~500 MPa, 7.0~15.0% and 23.9~24.2 MS/m, respectively, and the fracture toughness in L-T, T-L and S-L direction being 33.5~39.5, 25.5~27.0, 23.0~24.5 MPa.m1/2, respectively, and the EXCO rating being EA.

DSC and TEM Study of Al-Cu-Mg-Ag Alloy Ageing at Low and Elevated Temperature

Microstructural characterization of Al-Cu-Mg-Ag alloy ageing at low and elevated temperature were investigated by differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The results show that the precipitation sequence is significantly influenced by the ageing temperature. With prolonging of ageing at 65°C, G.P. zones on the plane of {100}α separates out with no precipitation of Ω phase. After 10h ageing at 160°C,the phase of Ω separates out and dominant the microstructure, while a small quantity of θ′separates out as well.

Microstructure and Porous Defects of a Spray-Formed and Hot Worked 7000 Aluminum Alloy

The evolution of microstructure and porous defects of a spray-formed 7000 Aluminum alloy is researched in this paper. The spray-formed alloy is treated by hot isostatic pressing (HIP), homogenization, hot extrusion, solution and aging treatment. Metallographic microscope, scanning electron microscope (SEM) and tensile test are used to research the microstructure and mechanical properties. The results show that, there are two kinds of porous defects in spray-formed alloy, which has gas and no gas. The porous defects of spray-formed ingot can be mostly eliminated by HIP and hot extrusion. After solution and aging treatment, the tensile strength and elongation reach 757MPa and 10.2%, respectively.

Microstructural Characteristics and Mechanical Properties of Spray-Deposited Mg-Gd-Y-Zr Alloy

In this study, Mg-6.8Gd-4.5Y-0.5Zr alloy was fabricated by the spray atomization and deposition technique. The microstructure and mechanical properties of the alloy were studied using optical microscopy, scanning/transmission electron microscopy, X-ray diffraction, and tensile tests. The secondary phases in the microstructure of the spray-deposited alloy were examined. The tensile test results indicate that the spray-deposited Mg-6.8Gd-4.5Y-0.5Zr alloy displays superior tensile strength due to grain refinement and the presence of precipitating strengthening phases.

Morphologies and Formation Mechanism of Interconnected Pores in a Spray Formed 7XXX Aluminum Alloy

In this paper, Al-Zn-Mg-Cu alloys were produced through spray forming technique. Microstructures of interconnected porosity defects in spray-deposited preforms were characterized by means of field emission scanning electron microscopy (FESEM). The formation mechanisms of different types of interconnected pores were investigated. The densification of deposited alloy preforms with interconnected pores was also analyzed. Interconnected pores in deposited alloys may be classified into four types, interconnected pores between interstices, between gas pores, between interstices and gas pores, and interconnected pores associated with solidification shrinkage, according to morphology and formation mechanism.

Improved Paint Baking Response of a Novel Al-Mg-Si Alloy Automotive Body Panels by Adding Zn Element and Pre-Ageing Matching

In the present work, the microstructure and properties of a novel Al-0.92Mg-0.78Si alloy with adding Zn element were investigated by electron back scattering diffraction (EBSD), transmission electron microscopy (TEM), high transmission electron microscopy (HREM), mechanical properties tests and Erichsen test. The alloy sheet was cold-rolled to about 1mm, then solution treated at 545 °C for 30mins, and immediately water quenched. After solution treatment, the alloy was pre-aged at 140 °C for 10mins. The average grain size of the alloy was about 20μm. The yield stress and elongation of pre-aged alloy was 137MPa and 30% respectively. The IE value of the alloy was 8.6mm. After paint baking at 170 °C for 30mins, the increment of yield stress was about 100MPa. The GP(II) zones were formed in the alloy during paint baking process through adding Zn element, which should play a very important role for improving paint hardening response significantly. GP(II) zones and η ́ phases were formed after artificial ageing at 170 °C for 10h.

Quench Sensitivity and Quench-Induced Precipitation in High Strength 7xxx Series Aluminum Alloys

This paper investigates the quench sensitivity of some selected 7xxx series Al alloys based on a Jominy End Quench method. The precipitate microstructures as a function of cooling rate during quenching are also characterized by using transmission electron microscopy (TEM). The results indicated that quench sensitivity and therefore the mechanical properties inhomogeneity in large plates or forgings can be predicted more accurately by the simultaneous combination of hardness and electrical conductivity measurements based on Jominy end quench. The hardness drop and conductivity increase in the novel alloy following a low cooling rate are much reduced compared to AA7050 and 7B04 because of a lower sensitivity to quench-induced precipitation on dispersoids. The novel alloy exhibited the least quench sensitivity, and the 7B04 Al alloy was the most quench sensitive. If the 90% of the maximum hardness is defined as the depth of quenching, the depth of 7B04 Al alloy, AA7050 through Jominy end quenching is about 20 and 55 mm respectively. Meanwhile, the depth of greater than 150 mm is achievable in the novel alloy, and hence it can be recommended to fabricate large section plates or forgings without compromising properties in the center of the part after a slow cool.