Exploration of Trade-Off Between Elastic Modulus and Strength of Mg–Gd–Y–Nd–Zr Alloy by Regulating Intermetallic Phases Through Si Addition

Liqun Guan,Yunlai Deng,Yaofeng Luo,An Luo,Xiaobin Guo 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10

In this study, low-cost Si was added to an Mg–8Gd–4Y–1Nd–0.5Zr alloy to regulate the intermetallic phases. The mechanicalproperties of 0, 0.5, and 1.0 wt% Si-added alloys were studied to explore the trade-off between the elastic modulus andstrength. The microstructures were characterized through metallographic microscopy, scanning electron microscopy applyingenergy dispersive spectroscopy, and transmission electron microscopy. The microstructures demonstrated that Y5Si3and GdSi phases formed and consumed the solid soluble Gd and Y elements, thus reducing the amount of precipitation andincreasing the size of the β′ phase. Correlations between the elastic modulus and the intermetallic phase indicated that theY5Si3and GdSi phases formed by the addition of Si were the mainly responsible for the improvement in the elastic modulus. The change in strength through the addition of Si was calculated, and the results revealed that such an addition could increasethe elastic modulus but with a reduction in the alloy strength. The addition of 0.5 wt% Si alloy resulted in a relatively highcomprehensive performance, with an elastic modulus of 46 GPa, a tensile strength of 278 MPa, a yield strength of 226 MPa,and an elongation of 4.9% under a cast-T6 state.

Effect of the Cross Accumulative Roll Bonding on the Corrosion Behaviour of AA6082/AA7204 Composite Sheets

Manfa Yuan,Yunlai Deng,Sen Lin,Xiaobin Guo,Yuankang Xie 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9

In this work, Al–Mg–Si/Al–Zn–Mg laminated composite sheets were successfully produced first time by combining AA6082and AA7204 sheets through the cross accumulative roll bonding process. Two different starting materials were rolling bondedas alternate layers up to 8 rolling cycles with 408 °C pre-heating for 20 min before each cycle. In-situ corrosive surface wascharacterized by the electron backscattered diffraction to study the relationship between the grain orientation and the corrosionbehavior of Al–Mg–Si/Al–Zn–Mg composite sheets. 78.2% of the volume fraction of S-type ({123} <634>) texture,46.0% of R-Cubic-type ({001} <110>) texture and 18.8% of Brass-type ({110} <112>) texture reduced during in situ corrosivetests. Corrosion results indicated that the excellent corrosion resistance mainly contributed from grains near Brass-typetexture ({110} <112>). As the volume fraction of the Brass-type ({110} <112>) texture distributed in the Al–Zn–Mg alloyaround the interface increased from 0.18 to 4.16% with the rolling reduction increased from 93.7 to 99.2%, the corrosionresistance of the laminated rolling material improved.

Influence of Asymmetric Rolling Process and Thickness Reduction on the Microstructure and Mechanical Properties of the Al–Mg-Si Alloy

Xuehong Xu,Yunlai Deng,Xiaobin Guo,Qinglin Pan 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7

The influence of the asymmetric rolling process (ASR) and thickness reduction on the microstructure and mechanical propertiesof Al–Mg–Si alloys is studied. The specimens of the ASR and higher thickness reduction show higher strength (both theultimate tensile strength and yield strength) and lower elongation (El). However, both the strength and El are reduced withthe increase of the rotation speed ratio (ω1/ω2) in the specimens treated by the ASR. The grain size, density of dislocations,volume fraction of deformation texture and number density of precipitates are the main reasons causing the difference instrength and El. The increment in strength is mainly due to the increase of deformation texture, density of dislocations duringthe cold rolling and number density of precipitates formed during subsequent ageing. The reduction of volume fractionof deformation texture and number density of precipitates are responsible for the decrease of the strength in the specimenstreated by the ASR. The high-density dislocations in turn provide little room for the accumulation of dislocations and thereforereduces the EI.

Precipitation Behavior in Al-Zn-Mg-Cu Alloy After Direct Quenching

Shengdan Liu,Chengbo Li,Yunlai Deng,Xinming Zhang,Qiming Zhong 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.2

The precipitation behavior in an Al-6.8Zn-1.9Mg-1.0Cu-0.12Zr alloy after direct quenching from solutionheat treatment temperature of 470 °C to 205-355 °C was investigated by means of hardness tests, electricalconductivity tests, and transmission electron microscopy. At temperatures below 265 °C, the hardnessincreased gradually to a peak value and then decreased rapidly with time. At 265 °C, the hardness wasalmost unchanged within the initial 2000 s and then decreased gradually. At higher temperatures, the hardnessdecreased slowly with time. The electrical conductivity started to increase after a certain period oftime and then tended to maintain a constant value at all temperatures. Microstructure examination indicatedheterogeneous precipitation of the η phase at grain boundaries and inside grains during holding at205 °C and 325 °C. Based on the electrical conductivity data, the precipitation kinetics could be describedquite well by the Johnson-Mehl-Avrami-Komolgorov relationship with a n value varying between 0.78 and1.33. The activation energy was estimated to be about 44.9 kJ/mol, which is close to that expected for a dislocationdiffusion mechanism. Time-temperature-transformation diagrams were constructed and the nosetemperature ranged from 295 °C to 325 °C.

Mechanism of Ductility Enhancement of the Mg-8Gd-4Y-1Nd-0.5Si Alloy by Multi-Directional Forging Process before Extrusion

Manfa Yuan,Jin Zhang,Yunlai Deng,Xiaobin Guo,Liqun Guan 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.5

Noteworthy ductility Mg-8Gd-4Y-1Nd-0.5Si (wt.%) alloy with a strong non-basal texture was developed by 12 passes ofmulti-directional forging (MDF) combine with extrusion. The slip trace analysis indicated that deformation mechanism after3 passes of MDF and extrusion were basal < a > , pyramidal < a > and pyramidal < c + a > slips. The intensity of non-basaltexture increased from 5.37 to 8.03 with the MDF passes increased from 3 to 12, which means grain orientation tends tobe more consistent and makes the basal < a > slips easy to pass through grain boundaries to accommodate ductility. Withmore basal < a > slips crossing the grain boundaries, dislocation interaction in grain interior caused stress accumulation,exceeding the critical shear stress (CRSS) of slips with low schmidt factor (SF), and multiple slips appeared. The activationof slip cross grain boundary and multiple slip improved the elongation from 14.7% to 25.6% of MDFs-extruded Mg-8Gd-4Y-1Nd-0.5Si alloy.

Critical Quenching Rate for High Hardness and Good Exfoliation Corrosion Resistance of Al-Zn-Mg-Cu Alloy Plate

Dongfeng Li,Bangwen Yin,Yue Lei,Shengdan Liu,Yunlai Deng,Xinming Zhang 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.2

By means of the end-quenching technique, we investigated the relationship between quenching rate and hardness as well as exfoliation corrosion rating for Al-2.21 Zn-3.59 Mg-0.45 Cu-0.038 Zr (at%) alloy plate. In order to achieve an exfoliation corrosion rating of P or EA, the quenching rate must be greater than approximately 460 °C/min and 300 °C/min, respectively, and the drop degree in hardness should simultaneously be lower than approximately 2.0% and 3.5%, respectively. The results of microstructural and microchemical examination using a scanning transmission electron microscope indicate that a lower quenching rate leads to a higher content of Zn, Mg, and Cu in the grain-boundary particles and a greater width of precipitate-free zones near grain boundaries; therefore, grain-boundary particles with Zn and Mg contents less than approximately 13.39% and 10.23% (at%), respectively, and precipitate-free zones near grain boundaries with widths less than about 107 nm can contribute to an exfoliation corrosion rating better than EA. The amount of quench-induced η- phase particles, which lead to lower hardness, increases with decreasing quenching rate, and the area fraction of these particles is approximately 2.9% at a quenching rate of 300 °C/min.