F. Huang
材料科学技术（英）
Microstructure and hardness were investigated in pure Al samples with different purities (5N: 99.999%, 4N: 99.993%, and 2N: 99.7% in weight) subjected to dynamic plastic deformation at cryogenic temperatures. The saturated sizes of refined grains/subgrains in these samples induced by plastic deformation are about 240 nm without an obvious impurity effect, but the dislocation density in 2N Al is evidently higher than that in other samples. Boundary misorientations for 5N and 4N Al are below 10° with average values of 2-3°, while the average misorientation for 2N Al is obviously larger, being about 14°. Microhardness of LNT-DPD 2N Al is higher than that of 5N and 4N Al, owing to the enhanced dislocation density as their grain/subgrain sizes are almost identical.
关键词:
Aluminum
Jitai NIU
,
Lihong HAN
,
Chonghao WOO
材料科学技术（英）
Grain growth and grain boundary sliding are the two main superplastic deformation mechanisms. In the paper, simulation work is focused on the sliding of a Σ13 (111) symmetric twist coincidence grain boundary, a Σ13 (110) asymmetric tilt coincidence grain boundary, and a Σ3 (110) symmetric tilt coincidence grain boundary in Al, and the energies of grain boundary for each of equilibrium configurations are computed. An embedded atom method (EAM) potential was used to simulate the atomic interactions in a bicrystal containing more than 2000 atoms. At 0 K, the relationships between total potential energy and time steps for 3 (111) symmetric twist coincidence grain boundary and Σ3(110) symmetric tilt coincidence grain boundary during sliding at 2 m/s represent the periodic characteristic. However, the relationship between total potential energy and time steps for Σ13 (110) asymmetric tilt coincidence grain boundary represents the damp surge characteristic. It is found that grain boundary sliding for Σ3 (110) symmetric tilt coincidence grain boundary is coupled with apparent grain boundary migration.
关键词:
Aluminum
,
null
,
null
,
null
C.Y. Choi D.C. Kim D.G. Nam Y.D. Kim Y.D. Park
材料科学技术（英）
Currently, in the automotive industry, joining of the aluminum alloys with the steel is a crucial problem to be solved. Conventional joining techniques including resistance spot and gas metal arc welding are not acceptable for those applications due to a number of metallurgical problems. The investigation was carried out to develop the hybrid joining process combining the resistance spot welding and brazing. In this study, an attempt was made to apply hybrid process to the joining of dissimilar sheet metals, Al-Mg-Si (6000 series) alloy and low carbon steel sheet. Hybrid process (resistance spot weld/brazing) using filler metal was found to be effective to overcome the incompatibility between aluminum alloy and steel. Although hybrid joining process of Al alloy sheet and steel sheet did not produce acceptable bond strength, it was proved to have reasonable interfacial
bond layer if the optimal process condition was applied.
关键词:
Hybrid joining
,
Aluminum
,
Steel
,
Welding
Yu CHEN
材料科学技术（英）
A new type of hot-rolled transformation induced plasticity (TRIP) steel with 2.3%Al was developed to replace conventional Si-bearing TRIP steel to improve surface quality of the steel sheet. The relationship between retained austenite volume fraction and hot-rolling processing was researched by Gleeble-2000 thermo-dynamic test for the Al-bearing steel. The experimental result showed that aluminum played an important role on retaining austenite and the volume fraction increased from 4.4% to 7.5% as coiling temperature increased from 350℃ to 450℃, while coiling temperature had a stronger effect on retaining austenite than finishing rolling temperature.
关键词:
Aluminum
,
retained
,
austenite
,
coiling
,
temp
S.Billard
,
E.Meslin
,
G.F.Dirras
,
J.P.Fondère
,
B.Bacroix
材料科学技术（英）
Commercial purity Al has been processed by hot isostatic pressing consolidation of nanopowders. The resulting bulk material contained a small fraction of microcrystalline grains (>300 nm) embedded in a matrix of ultrafine grains (150 nm). The mechanical properties under compressive tests at various temperatures and at a strain rate of 2×10－4 s－1 have been investigated. At room temperature a brief hardening was observed followed by a stagnation of the flow stress up to failure. From 150 to 200℃ softening occurred after a short hardening stage. A change in the behavior showed up at 300℃: a quasi perfect plasticity was observed subsequently to a yield point. The major deformation mechanisms include dynamic recovery, grain fragmentation and sliding. Besides, when tested up to rupture at elevated temperature filament formation where observed at the fracture surface. The formation mechanism of the filaments is possibly linked to the presence of a viscous-like phase at grain boundaries.
关键词:
Aluminum
,
null
,
null
,
null
F. Huang
材料科学技术（英）
Microstructure and hardness were investigated in pure Al samples with different purities (5N: 99.999%, 4N: 99.993%, and 2N: 99.7% in weight) subjected to dynamic plastic deformation at cryogenic temperatures. The saturated sizes of refined grains/subgrains in these samples induced by plastic deformation are about 240 nm without an obvious impurity effect, but the dislocation density in 2N Al is evidently higher than that in other samples. Boundary misorientations for 5N and 4N Al are below 10° with average values of 2-3°, while the average misorientation for 2N Al is obviously larger, being about 14°. Microhardness of LNT-DPD 2N Al is higher than that of 5N and 4N Al, owing to the enhanced dislocation density as their grain/subgrain sizes are almost identical.
关键词:
Aluminum
M.Abou Zied
,
null
材料科学技术（英）
Microstructure and mechanical properties of ball-milled Al-8 wt pct Ni ribbon have been investigated by X-ray diffraction (XRD) and continuous Vickers hardness test, respectively. The results indicate that, the main phases of this alloy are α-Al and orthorhombic-Al3Ni. The lattice parameter of α-Al increases with increasing milling time. From the elastic constant of Al, the average contrast factors of the (111), (200), (220), (311) and (222) Bragg0s reflections for pure edge and pure screw dislocations in fcc crystals with a/2<110>{111} slip system were calculated. The average grain size and dislocation parameters as a function of milling time have been investigated using the modified Williamson-Hall plot and the Warren-Averbach equation, respectively. An attempt has been made to correlate the micro-hardness of milled ribbon with their grain size through the Hall-Patch relationship: HV0:01 = 742.45 < D >-1/2 +401.55 (kg/mm2).
关键词:
Aluminum
,
null
,
null
,
null
Chang-Seog Kang
,
Jae-Ik Cho
,
Chang-Yeol Jeong
,
Se-Weon Choi
,
Young-Chan Kim
材料科学技术（英）
Silicon-based aluminum casting alloys are known to be one of the most widely used alloy systems mainly due to their superior casting characteristics and unique combination of mechanical and physical properties. However, manufacturing of thin-walled aluminum die-casting components, less than 1.0 mm in thickness, is generally known to be very difficult task to achieve aluminum casting alloys with high fluidity. Therefore, in this study, the optimal die-casting conditions for producing 297 mm×210 mm×0.7 mm thin-walled aluminum component was examined experimentally by using 2 different gating systems, tangential and split type, and vent design. Furthermore, computational solidification simulation was also conducted. The results showed that split type gating system was preferable gating design than tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. It was also found that proper vent design was one of the most important factors for producing thin-wall casting components because it was important for the fulfillment of the thin-wall cavity and the minimization of the casting distortion.
关键词:
Aluminum
,
null
,
null
,
null
C.Y. Choi D.C. Kim D.G. Nam Y.D. Kim Y.D. Park
材料科学技术（英）
Currently, in the automotive industry, joining of the aluminum alloys with the steel is a crucial problem to be solved. Conventional joining techniques including resistance spot and gas metal arc welding are not acceptable for those applications due to a number of metallurgical problems. The investigation was carried out to develop the hybrid joining process combining the resistance spot welding and brazing. In this study, an attempt was made to apply hybrid process to the joining of dissimilar sheet metals, Al-Mg-Si (6000 series) alloy and low carbon steel sheet. Hybrid process (resistance spot weld/brazing) using filler metal was found to be effective to overcome the incompatibility between aluminum alloy and steel. Although hybrid joining process of Al alloy sheet and steel sheet did not produce acceptable bond strength, it was proved to have reasonable interfacial
bond layer if the optimal process condition was applied.
关键词:
Hybrid joining
,
Aluminum
,
Steel
,
Welding
Weimin MAO
,
Dong LI
材料科学技术（英）
The image stress of straight screw dislocations parallel to the medium surface covered by thin heterogeneous films was analyzed and deduced, in order to calculate the image shear stress. The relationship between image stress and distance from the screw dislocation to the interface of pure aluminum and its oxide covering was calculated based on the analysis. It was shown quantitatively that a sign conversion of the image stress appears in the case of thin oxide covering, while dislocation would pile up near the interface because of the possible slips of the screw dislocations induced by the image stress, which might break down the very thin oxide covering. Further investigation on edge dislocations or other dislocation configurations need to be done.
关键词:
Dislocation
,
null
,
null
,
null
,
null
,
null
,
null
