H. Jafari
金属学报(英文版)
doi:10.1016/S1006-7191(08)60115-5
Due to their high specifc strength and low density, magnesium alloys are widely used in many weight-saving applications. This research is aimed at investigating the microstructure and hardness of commercial AZ63 alloy specimens subjected to two diferent thermomechanical treatments (TMTs). For the first TMT, after solution treated at the temperature of 380 ℃ for 20 h, AZ63 alloy specimens were 5% cold worked by rolling process followed by ageing at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. In the second TMT, the specimens were solution treated at the temperature of 380 ℃ for 20 h, underwent 2% cold worked and quenched in water of 0 ℃. Half of the specimens were then 2% cold worked whilst the rest were rolled to 8% cold worked. All the specimens were then aged at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. Optical microscope was used to analyze the microstructures of the specimens. Hardness test was too conducted to measure the effect of the treatments on the specimens. Results show that two-step aging enhances the hardness of the specimens due to the distribution of the Beta-phase (Mg17Al12) in the alloy matrix. The results also reveal that, the best hardness from the first TMT was produced by specimen that was pre-aged at 150 ℃ whereas, in the second TMT, aging at 250 ℃ exhibited the best hardness values.
关键词:
Thermomechanical treatment
,
Magnesium
,
Cold work
,
Aging
,
AZ63
H. Keshmiri
材料科学技术（英文）
Duplex stainless steels (DSS) with ferritic{austenitic microstructures offer good combination of resistance to pitting corrosion and high strength that are not concomitantly attainable using conventional single phase austenitic or ferritic stainless steels. The DSS used in this investigation was 2205 alloy having a stable microstructure consisting of about 45% ferrite and 55% austenite at ambient temperature. In order to investigate aging behavior of this steel and the influences on mechanical properties, different aging treatments were conducted at temperatures of 350−950°C for various aging time of 15, 30, 60 and 180 min. The aged specimens were subjected to impact testing and hardness measurements. Finally, the changes in microstructure due to aging were studied by optical and scanning electron microscopy. The results showed that aging at temperatures lower than 550°C for different time had negligible effects on mechanical properties. Besides, no considerable changes in term of precipitation of harmful intermetallic particles were observed in microstructure below this temperature. However, a critical temperature range, 550−650 °C, was introduced here. Aging in this range led to a significant decrease in toughness and notable increase in hardness. The formation of intermetallic phases such as σ was recognized as the major reason for the observed changes.
关键词:
Duplex stainless steel
,
null
,
null
,
null
A. Momeni K. Dehghani
材料科学技术（英文）
In this research, aging treatments at temperatures of 800 and 900°C for different aging time of 5{60 min were conducted on solution treated as well as hot worked samples of 2205 dual phase stainless steel. The effect of aging treatment on precipitation of intermetallic phases was investigated in undeformed specimens and those subjected to hot deformation with different strain rates of 0.001−1 s−1. It was found that σ precipitation increased by hot working. It was also concluded that the volume fraction of phase increased with deformation temperature and decreased with strain rate. The precipitation of intermetallic phases (i.e. σ and χ) was analyzed by an Avrami-type kinetics equation of %(σ+χ)=A(1-exp(-ktn)) and the values of n and ln k were estimated for different thermomechanical regimes. The values of n were assessed to increase from 0.4 to 1 with strain rate in the studied range. Otherwise, It was also understood that ln k decreased with strain rate. Microstructural observations by means of optical microscopy and scanning electron microscopy showed that σ particles mostly nucleated at the ferrite-austenite interfaces. But no sign of Â-phase could be seen. This fortified the idea of certain literature that Â-phase always forms at early stages of aging and consumes through the precipitation of σ.
关键词:
Duplex stainless steel
,
Hot Working
,
Sigma Phase
,
Secondary Phase
Ning Zhao
材料科学技术（英文）
The wetting property of (Sn-9Zn)-2Cu (wt pct) on Ni substrate and the evolution of interfacial microstructure in (Sn-9Zn)-2Cu/Ni joints during soldering as well as isothermal aging were studied. The wetting ability of eutectic Sn-9Zn solder on Ni substrate was markedly improved by adding 2 wt pct Cu into this solder alloy. Plate-like Cu5Zn8 intermetallic compounds (IMCs) were detected in (Sn-9Zn)-2Cu solder matrix. A continuous Ni5Zn21 IMC layer was formed at (Sn-9Zn)-2Cu/Ni interface after soldering. This IMC layer kept its type and integrality even after aging at 170°C for up to 1000 h. At the early aging stage (before 500 h), the IMC layer grew fast and its thickness followed a linear relationship with the square root of aging time. Thereafter, however, the thickness increased very slowly with longer aging time. When the joints were aged for 1000 h,
a new IMC phase, (Cu,Ni)5Zn8, was found in the matrix near the interface. The formation of (Cu,Ni)5Zn8 phase can be attributed to the di®usion of Ni atoms into the solder matrix from the substrate.
关键词:
Lead-free solder
,
null
,
null
,
null
A. Momeni K. Dehghani
材料科学技术（英文）
In this research, aging treatments at temperatures of 800 and 900°C for different aging time of 5{60 min were conducted on solution treated as well as hot worked samples of 2205 dual phase stainless steel. The effect of aging treatment on precipitation of intermetallic phases was investigated in undeformed specimens and those subjected to hot deformation with different strain rates of 0.001−1 s−1. It was found that σ precipitation increased by hot working. It was also concluded that the volume fraction of phase increased with deformation temperature and decreased with strain rate. The precipitation of intermetallic phases (i.e. σ and χ) was analyzed by an Avrami-type kinetics equation of %(σ+χ)=A(1-exp(-ktn)) and the values of n and ln k were estimated for different thermomechanical regimes. The values of n were assessed to increase from 0.4 to 1 with strain rate in the studied range. Otherwise, It was also understood that ln k decreased with strain rate. Microstructural observations by means of optical microscopy and scanning electron microscopy showed that σ particles mostly nucleated at the ferrite-austenite interfaces. But no sign of Â-phase could be seen. This fortified the idea of certain literature that Â-phase always forms at early stages of aging and consumes through the precipitation of σ.
关键词:
Duplex stainless steel
,
Hot Working
,
Sigma Phase
,
Secondary Phase
Omyma Hassan Ibrahim Ibrahim Soliman Ibrahim Tarek Ahmed Fouad Khalifa
材料科学技术（英文）
In the present study, the effect of aging heat treatment at 650, 750, and 850°C on the impact toughness of 316L austenitic stainless steel, 2205 duplex stainless steel and their weldments has been investigated. Welding process was conducted using the TIG (tungsten inert gas) welding technique. Instrumented impact testing, at room temperature, was employed to determine the effect of aging treatment on the impact properties of investigated materials. Aging treatment resulted in degradation in the impact toughness as demonstrated by the reduction in the impact fracture energy and deformation parameters (strain hardening capacity, fracture deflection, and crack initiation and propagation energy). The degree of embrittlement was more noticeable in duplex stainless steel parent and weld-metal than in 316L stainless steel and became greater with the
increase of aging temperature. The degradation in impact toughness was discussed in relation to the observed precipitation of the intermetallic sigma phase in the microstructure of the stainless steel weldments and the corresponding fracture surface morphology.
关键词:
Austenitic and duplex stainless steels
,
Ageing
,
Instrumented impact toughness
Omyma Hassan Ibrahim Ibrahim Soliman Ibrahim Tarek Ahmed Fouad Khalifa
材料科学技术（英文）
In the present study, the effect of aging heat treatment at 650, 750, and 850°C on the impact toughness of 316L austenitic stainless steel, 2205 duplex stainless steel and their weldments has been investigated. Welding process was conducted using the TIG (tungsten inert gas) welding technique. Instrumented impact testing, at room temperature, was employed to determine the effect of aging treatment on the impact properties of investigated materials. Aging treatment resulted in degradation in the impact toughness as demonstrated by the reduction in the impact fracture energy and deformation parameters (strain hardening capacity, fracture deflection, and crack initiation and propagation energy). The degree of embrittlement was more noticeable in duplex stainless steel parent and weld-metal than in 316L stainless steel and became greater with the
increase of aging temperature. The degradation in impact toughness was discussed in relation to the observed precipitation of the intermetallic sigma phase in the microstructure of the stainless steel weldments and the corresponding fracture surface morphology.
关键词:
Austenitic and duplex stainless steels
,
Ageing
,
Instrumented impact toughness
