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1.
The quench sensitivity of a cast Al-7 wt pct Si-0.6 wt pct Mg alloy was characterized by tensile tests and scanning electron
microscopy. Specimens were cooled from the solution treatment temperature following 58 different cooling paths including interrupted
and delayed quenches. Analysis of the microstructure showed that quench precipitates were Mg2Si (β), which nucleated heterogeneously on Si eutectic particles as well as in the aluminum matrix, presumably on dislocations.
The quench sensitivity of the alloy’s yield strength was modeled by multiple C-curves, using an improved methodology for quench
factor analysis. The three C-curves used in the model represented loss of solute by (1) diffusion of Si to eutectic particles,
(2) precipitation of β on Si eutectic particles, and (3) precipitation of β in the matrix. The model yielded a R
2 of 0.994 and a root-mean-square error (RMSE) of 7.4 MPa. The model and the implications of the results are discussed in the
article.
This article is based on a presentation made in the symposium entitled “Simulation of Aluminum Shape Casting Processing: From
Design to Mechanical Properties,” which occurred March 12–16, 2006 during the TMS Spring Meeting in San Antonio, Texas, under
the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control
Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum
Committee. 相似文献
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Friction-stir (FS) processing was used to modify the coarse, fully lamellar microstructure of investment cast and hot isostatically
pressed (HIP’ed) Ti-6Al-4V. The effect of FS processing on mechanical properties was investigated using microtensile and four-point
bend fatigue testing. The tensile results showed a typical microstructure dependence where yield strength and ultimate tensile
strength both increased with decreasing slip length. Depending on the processing parameters, fatigue strength at 107 cycles was increased by 20 pct or 60 pct over that of the investment cast and HIP’ed base material. These improvements have
been verified with a statistically significant number of tests. The results have been discussed in terms of the resistance
of each microstructure fatigue crack initiation and small crack propagation. For comparison, a limited number of fatigue tests
was performed on α + β forged Ti-6Al-4V with varying primary α volume fraction and also on investment cast material heat treated to produce a bi-lamellar condition. 相似文献
4.
针对我国自主研制的新型Al-12.7Si-0.7Mg合金挤压型材,采用金相显微镜、扫描电镜及其附带的能谱分析仪以及拉伸实验研究了固溶温度对铝基体晶粒、合金相粒子尺寸、形状及数量以及挤压材力学性能的影响规律,结果表明:Al-12.7Si-0.7Mg合金挤压材基体中存在大量尺寸极其细小的点状Mg2Si相及大量微米级共晶Si粒子和少量微米级AlFeSi过剩结晶相;固溶温度从440℃升高至540℃,尺寸极其细小的点状Mg2Si相逐渐回溶入基体消失,微米级共晶Si颗粒及含AlFeSi的过剩结晶相粒子形状趋于球化,而铝基体晶粒呈现出略有长大的趋势,且共晶硅颗粒具有较明显的细化铝基体晶粒的作用;合金挤压材的强度及延伸率随固溶温度升高分别呈现出单调增大及总体下降的趋势;新型Al-12.7Si-0.7Mg合金挤压材比较适宜的固溶温度为520℃,合金挤压材经最佳固溶温度固溶水淬再经170℃×2.5 h时效处理后的Rp0.2≥279 MPa,Rm≥330 MPa,A≥9.9%。 相似文献
5.
共晶合金具有良好的激光焊接性能,为提高电子封装盖板用Al-12Si合金的强度并保持良好的热物理性能,采用喷射沉积与热压烧结技术制备Al-12Si合金,研究添加0.6%Mg对合金微观组织、力学性能和热物理性能的影响.结果表明,喷射沉积/热压烧结Al-12Si合金中Si相呈近球形颗粒,平均直径为(4.5±0.2)μm,均匀... 相似文献
6.
Hongseok Choi Milton Jones Hiromi Konishi Xiaochun Li 《Metallurgical and Materials Transactions A》2012,43(2):738-746
In this study, an ultrasonic cavitation based dispersion technique was used to fabricate Al-7Si-0.3Mg alloyed with Cu and
reinforced with 1 wt pct Al2O3 nanoparticles, in order to investigate their influence on the mechanical properties and microstructures of Al-7Si-0.3Mg alloy.
The combined addition of 0.5 pct Cu with 1 pct Al2O3 nanoparticles increased the yield strength, tensile strength, and ductility of the as-cast Al-7Si-0.3Mg alloy, mostly due
to grain refinement and modification of the eutectic Si and θ-CuAl2 phases. Moreover, Al-7Si-0.3Mg-0.5Cu-1 pct Al2O3 nanocomposites after T6 heat treatment showed a significant enhancement of ductility (increased by 512 pct) and tensile strength
(by 22 pct). The significant enhancement of properties is attributed to the suppression of pore formation and modification
of eutectic Si phases due to the addition of Al2O3 nanoparticles. However, the yield strength of the T6 heat-treated nanocomposites was limited in enhancement due to a reaction
between Mg and Al2O3 nanoparticles. 相似文献
7.
The influence of solidification rate on the solution-treatment response has been investigated for an Al-7Si-0.3Mg alloy and an Al-8Si-3Cu-0.5Mg alloy. The concentrations of Mg, Cu, and Si in the matrix after different solution-treatment times were measured using a wavelength dispersive spectrometer. All Mg dissolves into the matrix for the Al-Si-Mg alloy when solution treated at 803 K (530 °C) because the π-Fe phase is unstable and transforms into short β-Fe plates which release Mg. The Q-Al5Mg8Cu2Si6 phase do not dissolve completely at 768 K (495 °C) in the Al-Si-Cu-Mg alloy and the concentration in the matrix reached 0.22 to 0.25 wt pct Mg. The distance between π-Fe phases and Al2Cu phases was found to determine the solution-treatment time needed for dissolution and homogenization for the Al-Si-Mg alloy and Al-Si-Cu-Mg alloy, respectively. From the distance between the phases, a dimensionless diffusion time was calculated which can be used to estimate the solution-treatment times needed for different coarsenesses of the microstructure. A model was developed to describe the dissolution and homogenization processes. 相似文献
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Friction Stir Processing of Investment-Cast Ti-6Al-4V: Microstructure and Properties 总被引:1,自引:0,他引:1
A.L. Pilchak D.M. Norfleet M.C. Juhas J.C. Williams 《Metallurgical and Materials Transactions A》2008,39(7):1519-1524
Investment-cast titanium components are becoming increasingly common in the aerospace industry due to the ability to produce
large, complex, one-piece components that were previously fabricated by mechanically fastening multiple pieces together. The
fabricated components are labor-intensive and the fastener holes are stress concentrators and prime sites for fatigue crack
initiation. The castings are typically hot-isostatically-pressed (HIP) to close internal porosity, but have a coarse, fully
lamellar structure that has low resistance to fatigue crack initiation. The as-cast + HIP material exhibited 1- to 1.5-mm
prior β grains containing a fully lamellar α + β microstructure consistent with slow cooling from above the β transus. Friction stir processing (FSP) was used to locally modify the microstructure on the surface of an investment-cast
Ti-6Al-4V plate. Friction stir processing converted the as-cast microstructure to fine (1- to 2-μm) equiaxed α grains. Using micropillars created with a dual-beam focused ion beam device, it was found that the fine-grained equiaxed
structure has about a 12 pct higher compressive yield stress. In wrought products, higher strength conditions are more resistant
to fatigue crack initiation, while the coarse lamellar microstructure in the base material has better fatigue crack growth
resistance. In combination, these two microstructures can increase the fatigue life of titanium alloy castings by increasing
the number of cycles prior to crack initiation while retaining the same low-crack growth rates of the colony microstructure
in the remainder of the component. In the current study, high-cycle fatigue testing of investment-cast Ti-6Al-4V was performed
on four-point bend specimens. Early results show that FSP can increase fatigue strength dramatically.
This article is based on a presentation given in the symposium entitled “Materials Behavior: Far from Equilibrium” as part
of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred December 15–16, 2006 in Mumbai, India. 相似文献
12.
Single-pass friction stir processing (FSP) was used to increase the mechanical properties of a cast Mg-Zn-Zr-rare earth (RE)
alloy, Elektron 21. A fine grain size was achieved through intense plastic deformation and the control of heat input during
processing. The effects of processing and heat treatment on the mechanical and microstructural properties were evaluated.
An aging treatment of 16 hours at 200 °C resulted in a 0.2 pct proof stress of 275 MPa in the FSP material, a 61 pct improvement
over the cast + T6 condition. 相似文献
13.
S. H. Chowdhury D. L. Chen S. D. Bhole X. Cao P. Wanjara 《Metallurgical and Materials Transactions A》2013,44(1):323-336
This study was aimed at characterizing the microstructure, texture and tensile properties of a friction stir welded AZ31B-H24 Mg alloy with varying tool rotational rates and welding speeds. Friction stir welding (FSW) resulted in the presence of recrystallized grains and the relevant drop in hardness in the stir zone (SZ). The base alloy contained a strong crystallographic texture with basal planes (0002) largely parallel to the rolling sheet surface and $ \langle {11\bar{2}0} \rangle $ directions aligned in the rolling direction (RD). After FSW the basal planes in the SZ were slightly tilted toward the TD determined from the sheet normal direction (or top surface) and also slightly inclined toward the RD determined from the transverse direction (or cross section) due to the intense shear plastic flow near the pin surface. The prismatic planes $ (10\bar{1}0) $ and pyramidal planes $ (10\bar{1}1) $ formed fiber textures. After FSW both the strength and ductility of the AZ31B-H24 Mg alloy decreased with a joint efficiency in-between about 75 and 82 pct due to the changes in both grain structure and texture, which also weakened the strain rate dependence of tensile properties. The welding speed and rotational rate exhibited a stronger effect on the YS than the UTS. Despite the lower ductility, strain-hardening exponent and hardening capacity, a higher YS was obtained at a higher welding speed and lower rotational rate mainly due to the smaller recrystallized grains in the SZ arising from the lower heat input. 相似文献
14.
Yue Wu William A. Cassada Enrique J. Lavernia 《Metallurgical and Materials Transactions A》1995,26(5):1235-1247
High Si content in Al-Si alloys usually leads to the formation of coarse, brittle Si phase under slow solidification conditions.
In the present study, an Al-17Si-4.5Cu-0.6Mg (referred to hereafter as AS17) was synthesized using spray deposition to modify
the Si phase. In the spray deposition process, the master alloy of AS17 was atomized using N2 gas, and was deposited on a collecting substrate directly into a three-dimensional material. The microstructure and mechanical
behavior of the spray-deposited AS17 were studied using optical microscopy (OM) scanning electron microscopy (SEM), transmission
electron microscopy (TEM), X-ray diffraction, and tensile tests. The present results indicate that in the spray-deposited
AS17, the eutectic Si phase was modified from a “flakelike” morphology, characteristic of ingot metallurgy (IM) materials,
into a “particulate” morphology. The formation of the coarse primary Si blocks was suppressed. Moreover, the size and morphology
of Si particulates were found to have significant influences on the deformation behavior. During plastic deformation, extensive
fracture of Si occurred. The percentage of fractured Si increased with the increasing amount of plastic deformation and the
size of Si particulates. Finally, the room-temperature mechanical properties of the spray-deposited AS17 were compared with
its IM counterpart A390 (an IM alloy with identical composition as AS17). The strength and ductility of AS17 were improved
over those of A390. In the T6 condition, the yield strength and tensile elongation of AS17 were 503 MPa and 3.0 pct, respectively,
whereas those of A390 were 374 MPa and 1.3 pet, respectively. 相似文献
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《钢铁研究学报(英文版)》2016,(1):14-18
Al-Si-Fe-Cu-Mg alloy was prepared by spray deposition and was further processed by hot extrusion as well as T6heat-treatment.The results indicate that the microstructure of the deposited alloy is composed of primary Si particles with average size of less than 5μm,α-Al,Al_2CuMg,β-Al_5FeSi andδ-Al_4FeSi_2(rectangular shape),and no eutectic silicon is found due to the special solidification behavior.The age hardening curves reveal two peaks.The uniform ultimate tensile strength(UTS)and the elongation of the peak-aged Al-Si-Fe-Cu-Mg alloy are 468.3 MPa,0.61% at 298 Kand 267.4MPa,6.42% at 573 K,respectively.The fracture surfaces display brittle fracture morphology at 298 K,whereas it varies to mixture of brittle and ductile failure with increasing the temperature. 相似文献
17.
G. R. Cui D. R. Ni Z. Y. Ma S. X. Li 《Metallurgical and Materials Transactions A》2014,45(12):5318-5331
Friction stir processing (FSP) was applied to modify the microstructure of an as-cast A356 alloy. The effects of rotation rate, travel speed, in situ FSP pass, FSP direction, and artificial aging on microstructures and tensile properties were investigated. FSP broke up the coarse eutectic Si phase into 2.5 to 3.5 μm particles and distributed them homogeneously, and resulted in the dissolution of the coarse Mg2Si particles and the elimination of porosity, thereby improving both the strength and the ductility of the casting. Increasing the rotation rate was beneficial to breaking up and dissolving the particles, but it contributed little to eliminating the porosity. The travel speed did not affect the size of the particles apparently, but lower speed was beneficial to eliminating the porosity. 2-pass FSP showed an obvious advantage in the microstructure modification and tensile properties compared with the single-pass. However, a further increase of FSP passes only resulted in slight improvement. The FSP direction of the following pass did not show distinct effect on the microstructure and tensile properties. After post-FSP artificial aging, the strengthening phase (β″-Mg2Si) precipitated, which increased the strength and decreased the ductility of the FSP samples. 相似文献
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S. S. Babu J. Livingston J. C. Lippold 《Metallurgical and Materials Transactions A》2013,44(8):3577-3591
The feasibility of using high-strain rate (1.475 to 3.942 s?1) hot-torsion testing with a Gleeble® thermomechanical simulator was demonstrated for simulating microstructures consistent with friction stir processing (FSP) of Ti-6Al-4V. The tests were performed on α/β-processed base material at temperatures both above and below the β-transus. Various phenomena including the refinement of α- and β-grains, deformation-induced heating, and deformation instabilities were observed. These tests reproduced the range of microstructures that are observed under FSP processing conditions. The testing methodology can be used for generating constitutive material property equations relevant to computational FSP/friction stir welding models. 相似文献