Papers by Keyword: Quench Sensitivity

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Authors: Seong Taek Lim, Yong Yun Lee, Il Sang Eun
Abstract: An effort has been made to present optimum alloy designs of commercial 7175 and 7050 type alloys to be used in thick forgings with proper microstructures and properties. The effects of changing alloy constitutions, primarily [Zn+Mg+Cu] and Zn:Mg ratio, on the evolutions of the coarse equilibrium phases and age hardening response are investigated. As a result, equilibrium phases (M,T,S) are evolved depending on alloy constitutions and cooling rate following solutionizing. The formation of the T- and S-phases is effectively controlled in the novel alloys (dilute and with high Zn:Mg ratio). In the slow quench, the redesign promotes homogeneous precipitation of η-phases, leading to higher mechanical properties than conventional alloys. The novel alloys provide microstructural homogeneity and extended heating range, ensuring 7xxx thick forging applications.
Authors: Takeshi Saito, Calin D. Marioara, Jostein Røyset, Randi Holmestad
Abstract: The effect of cooling rate after solution heat treatment and its combination with 1% pre-deformation on precipitation hardening in two Al-Mg-Si alloys is investigated by transmission electron microscopy (TEM), and related to material hardness. Two alloys have been used, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes. A double peak hardness evolution during an isothermal heat treatment was observed with slow cooling after solution heat treatment. This effect was less pronounced in the Cu-added alloy. The 1% pre-deformation also made this effect less pronounced, but it led to faster initial hardness evolution and delayed over-aging. Maximum hardness was not influenced by cooling rate and the pre-deformation. Hardness was directly related to precipitate number densities.
Authors: Y.H. Kang, D. Wu, Rong Shi Chen, E.H. Han
Abstract: The effects of quenching rate on the microstructures and mechanical properties of the heat treatable Mg-4.2Y-2.3Nd-1.0Gd-0.6Zr (wt.%) (WE43) sand-cast alloy have been studied using a combination of mechanical testing, Vickers hardness testing, optical microscopy (OM) and scanning electron microscope (SEM). Two quenching conditions, either air quenching or 60°C water quenching, were employed. The results indicate that some precipitates have formed in the matrix and grain boundaries in the air-quenched solutionized alloy. And the Vickers hardness and yield strength (YS) is HV77 and 155 MPa, respectively, which is slightly more than the 60°C water-quenched solutionized alloy. However, the ultimate tensile strength (UTS) and yield strength (YS) of the peak-aged at 250°C (T6) of the two quenching conditions are both 273 MPa and 212 MPa, respectively. And they have similar age hardening curves at 250°C and the T6 microstructure. So the results indicate that in this work of quenching rate range WE43 alloy has few quench sensitivity effect.
Authors: T.F. Morgeneyer, Marco J. Starink, I. Sinclair
Abstract: Analysis of toughness in 6156 Al-Mg-Si-Cu sheet has been performed using enhanced Kahn tear tests on samples quenched at different rates, whilst microstructures of the samples have been assessed using differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Crack initiation energies were unaffected by changing water quench temperature from 20°C to 60°C, however a significant reduction was evident on air cooling. Crack propagation resistance was reduced for both 60°C water quenched and air cooled materials. The failure morphology of the air cooled material appears consistent with classical intergranular ductile failure. Coarse voiding and shear decohesion was prevalent in the 20°C water quenched material, whilst the 60°C water quenched material showed a mixture of transgranular and intergranular fracture modes. Changes in microstructure and precipitation behaviour resulting from reduced quenching rate were identified and related to the observed fracture behaviour, particularly in terms of precipitate free zone formation and the simultaneous presence of coarse particles at grain boundaries.
Authors: Takeshi Saito, Calin D. Marioara, Jostein Røyset, Randi Holmestad
Abstract: Quench sensitivity in two Al-Mg-Si alloys, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes, has been investigated using transmission electron microscopy (TEM) and corresponding material hardness. A two stage hardness evolution during an isothermal heat treatment was observed with slow cooling after solution heat treatment. This effect was less pronounced in the Cu-added alloy. However maximum hardness was not influenced by cooling rate, which could be related to higher precipitate number densities and volume fractions. Both alloys were over-aged faster in the slow cooling conditions.
Authors: Bai Qing Xiong, Xi Wu Li, Yon Gan Zhang, Zhi Hui Li, Bao Hong Zhu, Feng Wang, Hong Wei Liu
Abstract: 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.
Authors: Xin Yu Lu, Zhi Hui Li, Guo Jun Wang, Yon Gan Zhang, Bai Qing Xiong
Abstract: The quench sensitivity of 2D70 aluminum alloy was investigated by end-quenching. The effect of water temperature on quench sensitivity was studied by measuring the hardness and conductivity. The end-quenching characteristics of hardness and conductivity of 2D70 aluminum alloy under different water temperatures has been described. The end-quenching characteristics of 2D70 and 2124 alloy under the same condition have been compared and analyzed. The results show that the susceptibility of 2D70 alloy to quenching is slow and the differential effects of the water temperatures of 16°C and 30°C on end-quenching of this alloy are not obvious. The quench depth of the alloy is more than 150mm.
Authors: V.G. Davydov, L.B. Ber, V.N. Ananiev
Authors: Zhi Hui Li, Bai Qing Xiong, Yon Gan Zhang, Xi Wu Li, Feng Wang, Hong Wei Liu
Abstract: 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.
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