Authors: Yu Fan, Guo Hua Wu, Chun Quan Zhai
Abstract: With adding 2% strontium in AZ91D, the ultimate tensile strength and the elongation
increased by 10.3% and 55.3%, respectively. This is mainly caused by the refinement of the β phase
and the formation of Al4Sr strengthening phase. Furthermore, with adding 2% strontium in AZ91D
alloy, the weight loss corrosion rate in 5wt.% NaCl solution decreases to 0.048 mg·cm-2·d-1, which
was 33.8 % of the AZ91D corrosion rate. Therefore, the mechanical properties and corrosion
resistance of AZ91D could be improved by the addition of 2% strontium, which is due to the
refinement of Mg17Al12 phase and the formation of Al4Sr phase.
567
Authors: Peng Zhao, Qu Dong Wang, Chun Quan Zhai, Wen Jiang Ding
Abstract: Tensile and compressive creep properties of Mg-5wt.%Al-1wt.%Sr alloy produced by
gravity casting were investigated in this paper. Creep tests were carried out in the temperature range
from 125 °C to 200 °C and stress range from 35 to 85MPa. The second creep rate in tension is
significant different from that in compression, indicating that coarse-grained Mg-Al-Sr alloy exhibits
tension/compression asymmetric behavior. Moreover, the activation energies and stress exponent in
tension and compression are not the same, which suggest that creep mechanisms in tension and
compression are different.
171
Authors: Li Ming Peng, Peng Huai Fu, Hai Yan Jiang, Chun Quan Zhai
Abstract: Compact AM50 alloy components were cast by Low Pressure Die Casting (LPDC)
process. The microstructure and mechanical properties of cast components were investigated under
as-cast and heat treated states. It was found that the microstructure of LPDC AM50 is composed of
α-Mg and second phases - Mg17Al12 and Al8Mn5. Compared with Gravity die casting, LPDC AM50
alloy had much coarser grains and higher density, with smaller sizes and less content of second
phases. The density of AM50 alloy by LPDC process was ρ=1.7836g/cm3, with increase of 0.45%
based on Gravity die casting and much more increase compared with high pressure die casting. The
as-cast mechanical properties by LPDC process were: σ0.2=57.8Mpa, σb=192.3Mpa, δ=8.7%. These
of Gravity die casting were: σ0.2=53Mpa, σb=173.4Mpa, δ=8.1%. UTS in LPDC increased about
20MPa, with better YTS and Elongation. Compared with that of high pressure die cast AM50, the
YTS of LPDC was much lower, with comparable UTS and Elongation. The mechanical properties of
the heat treated AM50 alloy were still in the same level of as-cast state. AM50 alloy by LPDC process
is not necessary subjected to tempering treatment.
167
Authors: Peng Huai Fu, Li Ming Peng, Hai Yan Jiang, Chun Quan Zhai, X. Gao, Jian Feng Nie
Abstract: The microstructure of Mg-3wt%Nd-0.2wt%Zn-0.4wt%Zr (NZ30K) alloy after solution
treatment was investigated and several kinds of interesting phases containing zirconium were found
in this study. NZ30K was gravity cast using permanent die casting. After high tempering solution
treatment at 540°C, cluster particles were observed inside the grains under optical microscopy. The
detailed investigations were carried out on transmission electron microscopy (TEM). Four kinds of
precipitates were visible inside grains with different shapes: block-like, globular, short rod-like, long
rod-like. The block-like particle was identified as ZrH2 phase and the globular one was Zn2Zr3 phase.
The other two were still Zr-containing phases, which could not be identified to any of existed
compounds containing Zr. The formation of Zn-Zr compounds would probably be due to relative
high ratio of Zr to Zn in the center of grains. ZrH2 would be the results of reaction of zirconium with
H element during solution treatment, which probably came into the alloy during melting.
97
Authors: Yongjun Chen, Qu Dong Wang, Jianguo Peng, Chun Quan Zhai
Abstract: Experiments were conducted both to evaluate the potential for grain refinement, the subsequent mechanical properties at room temperature in samples of AZ31 Mg alloy and also to investigate the relationship between one-step and two-step high ratio extrusion (HRE). The one-step HRE was undertaken using a high extrusion ratio of 70:1 at 250, 300 and 350°C. And the two-step HRE was conducted with an extrusion ratio of 7 for the first step at 250, 300 and 350°C, followed by a second-step extrusion with an extrusion ratio of 10 at 250, 300 and 350°C. The initial grain size in the AZ31 ingot was 100μm and that after one-step HRE became similar to 5μm, after two-step HRE at 250, 300 and 350°C were 2, 4, 7μm, respectively, resulting in superior mechanical properties at ambient temperature. The microstructure of two-step HRE was finer and uniformer than that of one-step HRE and the strength of one-step and two-step HRE were similar, moreover, the elongation of one-step HRE was improved markedly than that of two-step HRE. Dynamic recrystallization and adjacent grain broking during HRE is introduced to explain the effects of one-step and two-step HRE on the microstructure and mechanical properties of AZ31 Mg alloy. The current results imply that the simple HRE method might be a feasible processing method for industry applications, and the multiply steps extrusion are effective to fabricate high strength of fine grained hcp metals.
865
Authors: Yu Fan, Guo Hua Wu, Hong Tao Gao, Chun Quan Zhai
Abstract: The effects of RE and Ca on the mechanical properties and corrosion behavior of AZ91 have been studied by Zwick electronic universal material testing machine, X-ray diffraction, corrosion test and polarization experiment. The results showed that the addition of RE and Ca could improve the mechanical properties and corrosion resistance of AZ91 alloys. The ultimate tensile strength of AZ91 with addition of 1%RE and 1%Ca increased by 15.9%. The addition of 1%RE in AZ91 made the corrosion rate decrease from 0.453mg·cm-2·d-1 to 0.178mg·cm-2·d-1. Furthermore,
with adding 1%Ca in AZ91+1%RE, the corrosion rate of AZ91 decreased to 0.086mg·cm-2·d-1 due to the formation of reticular Al2Ca phases, which acts as an effective barrier against corrosion.
869
Authors: Honghui Zou, Xiao Qin Zeng, Chun Quan Zhai, Wen Jiang Ding
Abstract: Microstructure and mechanical property changes brought by the addition of Nd element in Mg-5wt%Zn-2wt%Al alloy are investigated, results show Al element takes a priority to react with Nd element over Mg and Zn, forming binary phases Al2Nd or Al11Nd3, tensile test showed that the total elongation is improved by the addition of Nd, and the UTS is also elevated when the Nd content surpass 1wt%. With a larger Nd addition, the phase dominating grain boundary is Al11Nd3 phase.
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