The effect of thermal exposure on the mechanical properties of 2099-T6 die forgings, 2099-T83 extrusions, 7075-T7651 plate, 7085-T7452 die forgings, 7085-T7651 plate, and 2397-T87 plate aluminum alloys

Aluminum alloys 2099-T6 die forgings, 2099-T83 extrusions, 7075-T7651 plate, 7085-T7452 die forgings, 7085-T7651 plate, and 2397-T87 plate were thermally exposed at temperatures of 180 °C (350 °F), 230 °C (450 °F), and 290 °C (550 °F) for 0.1, 0.5, 2, 10, 100, and 1000 h. The purpose of this study was to determine the effect of thermal exposure on the mechanical properties and electrical conductivity of these alloys. The data shows that higher temperatures and longer exposure times generally resulted in decreased strength and hardness and increased percent elongation and electrical conductivity.     

Metallurgical Design of High-Performance GMAW Electrodes for Joining HSLA-65 Steel

A C++ algorithm was used to metallurgically design high-performance GMAW electrodes for joining HSLA-65 steel. The electrode design was based on: (1) a carbon content ≤0.06 wt.% for improved weldability, (2) a 5-15% lower A_r3 transformation temperature than HSLA-65 steel for enhanced strength and toughness, and (3) a desirable range of carbon equivalent number (CEN) for consistently overmatching the minimum specified tensile strength of HSLA-65 steel. The algorithm utilized a set of boundary conditions that included calculated A_r3, B_S, B_F, and M_S transformation temperatures besides CEN. Numerical ranges for boundary conditions were derived from chemical compositions of commercial HSLA-65 steel, substituting thermomechanical effects with weld solidification effects. The boundary conditions were applied in evaluating chemical composition ranges of the following three prospective welding electrode specification groups that offered to provide ≤0.06 wt.% carbon, a minimum transverse-weld tensile strength of 552 MPa (80 ksi), and a minimum CVN impact toughness of 27 J at −29 °C through −51 °C (20 ft lbf at −20 °F through −60 °F) in the as-welded condition: (1) ER80S-Ni1, (2) E90C-K3, and (3) E80C-W2. At ≤0.06 wt.% carbon, the algorithm returned over 3100 results for E90C-K3 that satisfied the boundary conditions, but returned no acceptable results for other two electrode specification groups. Results revealed that welding electrode designs based on an Fe-C-Mn-Ni-Mo system, containing 0.06 wt.% C, 1.6 wt.% Mn, 0.8 wt.% Ni, and 0.3 wt.% Mo that provide weld metals characterized by an A_r3 of 690 °C, a CEN of 0.29, and a (B_F − M_S) of 30 °C are expected to consistently overmatch the minimum specified tensile strength of HSLA-65 steel while offering a minimum CVN impact toughness of 41 J at −40 °C (30 ft lbf at −40 °F).     

热机械加工对2099铝锂合金挤压材组织与抗腐蚀性能的影响

采用金相组织观察、XRD分析、硬度和导电率测试等手段,研究了热机械加工(Thermo-Mechanical Processing, TMP)对2099铝锂合金挤压材组织、硬度、导电率、晶间腐蚀及剥落腐蚀性能的影响。结果表明：与经T83 (540 ℃/2 h固溶、3%预压缩、121 ℃/14 h + 181 ℃/48 h时效)热处理的2099铝锂合金挤压材相比,经TMP(540 ℃/2 h固溶、400 ℃/48 h过时效、约50%大应变变形、540 ℃/2 h再结晶/固溶)+(121 ℃/14 h + 181 ℃/48 h时效)处理的2099铝锂合金挤压材发生了明显的再结晶,硬度（HV）降低(从2006.2 MPa到1865.3 MPa),位错强化亦降低,但导电率和抗晶间腐蚀性能明显提高,同时抗剥落腐蚀性能也有所提高。结果表明,热机械加工是不显著降低2099铝锂合金挤压材硬度,但显著提高其抗晶间腐蚀性能的有效途径     

Yield Stress of 21-6-9 Stainless Steel Over Very Wide Ranges of Strain Rates and Temperatures

The yield strength of solution-annealed 21-6-9 austenitic stainless steel was determined over a wider temperature range (−195 to 1100 °C) and strain rate (10⁻⁴ to 10⁴ s⁻¹) than has been previously reported. The most noteworthy characteristic of the variation of yield stress with temperature was the dramatic decrease in yield strength from −195 to 300 °C. The strain-rate sensitivity exponent, m, was determined using strain-rate change tests. m dramatically increases at about 850 °C with increasing temperature and m is approximately independent of strain (structure). Hopkinson split-bar tests from ambient temperature to 750 °C indicate that the strain-rate sensitivity of 21-6-9 is not strongly influenced by the over eight orders of magnitude change in strain rate. This suggests that the mechanism(s) of plastic flow at the higher rates is similar to that at lower rates. This contention was corroborated by transmission electron microscopy. The yield stress shows grain-size dependency.     

Design of multistep aging treatments of 2099 (C458) Al-Li alloy

Multistep artificial aging treatments coupled with various natural aging times for aluminum lithium 2099 alloy (previously called C458) are discussed to obtain mechanical tensile properties in the T6 condition that match those in the T861 condition, having a yield strength in the range of 414–490 MPa (60–71 ksi), an ultimate strength in the range of 496–538 MPa (72–78 ksi), and 10–13% elongation. Yield and ultimate tensile strengths from 90–100% of the strength of the as-received material (in the T861 condition) were obtained. The highest tensile strengths were consistently obtained with two-step, low-to-high temperature artificial aging treatments consisting of a first step at 120 °C (248 °F) for 12–24 h followed by a second step between 165 and 180 °C (329–356 °F) for 48–100 h. These T6-type heat treatments produced average yield and ultimate strengths in the longitudinal direction in the range of 428–472 MPa (62.1–68.5 ksi) and 487–523 MPa (70.6–75.9 ksi), respectively, as well as lower yield strength anisotropy when compared with the as-received material in the T861 condition.     

Constitutive Analysis to Predict High-Temperature Flow Stress in 2099 Al-Li Alloy

采用高温等温压缩试验并利用修正后的流变曲线,研究了2099 Al-Li合金在变形温度为300~500℃,应变速率为0.001~10 s-1,变形量(真应变)为0.7条件下的流变行为。结果表明:可用包含Z参数的双曲正弦形式来表征变形温度和应变速率对2099 Al-Li合金热变形行为的影响;将应变作为影响因素,求解了不同应变量下的材料常数,并构建了考虑应变的本构模型;统计分析结果表明,除了在变形温度为300℃,应变速率为10 s-1之外,该模型能够很好的预测2099 Al-Li合金高温流变行为。     

Temperature and grain size dependence of superplasticity in a Zn−0.3wt.%Al alloy

The superplastic deformation behavior of quasi-single phase Zn-0.3 wt. %Al was investigated. A series of load relaxation and tensile tests was conducted at various temperatures ranging from RT (20 °C) to 200 °C. The recently proposed internal variable theory of structural superplasticity was applied. The flow curves obtained from load relaxation tests were shown to consist of contributions from interface sliding (IS) and accommodating plastic deformation. In the case of quasi-single phase Zn-0.3 wt.% Al alloy with an average agrain size of 1 μm, the IS behavior could be described as a viscous flow process characterized by a power index of M_g=0.5. A large elongation of about 1400% was obtained at room temperature and the strain rate sensitivity parameter was about 0.4. Although relatively large-grained (10 μm) single phase alloy showed a high value of strain rate sensitivity comparable to that of fine-grained alloy at very low strain rate range, IS was not expected from the analysis based on the internal variable theory of structural superplasticity at room temperature. As the temperature increased above 100 °C, however, the contribution from IS was observed at a very low strain rate range. A high elongation of ∼400% was obtained in a specimen of 10-μm-grain-size at 200 °C under a strain rate of 2×10⁻⁴/sec. Jointly appointed at Center for Advanced Aerospace Materials (CAAM)     

High-temperature deformation behavior and processing map of 7050 aluminum alloy re]20101008

The high-temperature deformation behavior and processing map of 7050 aluminum alloy were investigated by tensile tests conducted at various temperatures (340, 380, 420, and 460 °C) with various strain rates of 10⁻⁴, 10⁻³, 10⁻², and 0.1 s⁻¹. The results show that the instability region with a peak power dissipation efficiency of 100 % occurs at the low deformation temperature region of 340 °C to 380 °C and high strain rates (>10⁻³ s⁻¹). The 7050 aluminum alloy exhibited a continuous dynamic recrystallization domain with power dissipation efficiency of 35% to 60 % in the deformation temperature range of 410 °C to 460 °C and the strain rate range of 10⁻⁴–10⁻³ s⁻¹. The domain with a power dissipation efficiency of 35 % to 50 % occurring at high deformation temperatures and strain rates was interpreted to represent dynamic recovery. Dynamic recovery and continuous dynamic recrystallization provide chosen domains for excellent hot workability.     

The compression stress-strain behavior of Sn-Ag-Cu solder

The yield-stress behavior was investigated for the 95.5Sn-4.3Ag-0.2Cu (wt.%), 95.5Sn-3.9Ag-0.6Cu, and 95.5Sn-3.8Ag-0.7Cu ternary lead-free solders using the compression stress-strain test technique. Cylindrical specimens were evaluated in the as-cast or aged (125°C, 24 h) condition. The tests were performed at −25°C, 25°C, 75°C, 125°C, and 160°C using strain rates of 4.2×10⁻⁵s⁻¹ or 8.3×10⁻⁴s⁻¹. Specially designed Sn-Ag-0.6Cu samples were fabricated to compare the yield stress of the dendritic microstructure versus that of the equiaxed microstructure that occurs in this alloy. For more information, contact P.T. Vianco, Sandia National Laboratories, MS 0889, PO Box 5800, Albuquerque, New Mexico 87185; (505) 844-3429; e-mail ptvianc@sandia.gov.     

Fatigue and Fracture Characterization of HPDC AM6OB Magnesium Alloy at Cold Temperature

An investigation of the fatigue and fracture characterization of the high pressure die cast (HPDC) AM60B magnesium alloy at −40 °C temperature was conducted by means of the constant load amplitude fatigue test. The results demonstrated that low temperature had a significant influence on alloy’s fatigue life; the life increased at −40 °C temperature as compared to that at room temperature. The fracture surfaces of the tested specimens were observed under a scanning electron microscope (SEM) to further understand the fracture phenomenon at low temperature.     

Upper bound analysis of deformation and dynamic ageing behavior in elevated temperature equal channel angular pressing of Al-Mg-Si alloys

In the present study, the plastic deformation and dynamic strain ageing behavior of Al-6082 (Al-Mg-Si) alloy treated with elevated temperature equal channel angular pressing (ECAP) were investigated using upper bound analyses. Tensile tests were carried out over wide ranges of temperature and strain rate in order to evaluate the dynamic ageing conditions. ECAP processing was then experimentally performed at temperatures from room temperature up to 200 °C under various strain rates ranging between 10⁻⁴s⁻¹ and 10⁻¹s⁻¹. The upper bound analysis solutions and the experimental results are comparable. A theoretical dynamic ageing region was found to be in the temperature range of 90 °C to 260 °C, which is in agreement with the experimental observations in the temperature range of 75 °C to 175 °C.     

Effect of low temperatures on charpy impact toughness of austempered ductile irons

Impact properties of standard American Society for Testing Materials (ASTM) grades of austempered ductile iron (ADI) were evaluated at subzero temperatures in unnotched and V-notched conditions and compared with ferritic and pearlitic grades of ductile irons (DIs). It was determined that there is a decrease in impact toughness for all ADI grades when there is a decrease in content of retained austenite and a decrease in test temperature, from room temperature (RT) to −60 °C. However, the difference in impact toughness values was not so noticeable for low retained austenite containing grade 5 ADI at both room and subzero temperatures as it was for ADI grade 1. Furthermore, the difference in impact toughness values of V-notched specimens of ADI grades 1 and 5 tested at −40 °C was minimal. The impact behaviors of ADI grade 5 and ferritic DI were found to be more stable than those of ADI grades 1, 2, 3, and 4 and pearlitic DI when the testing temperature was decreased. The impact toughness of ferritic DI was higher than that of ADI grades 1 and 2 at both −40 °C and −60 °C. The impact properties of ADI grades 4 and 5 were found to be higher than that of pearlitic DI at both −40 °C and −60 °C. The scanning electron microscopy (SEM) study of fracture surfaces revealed mixed ductile and quasicleavage rupture morphology types in all ADI samples tested at both −40 °C and −60 °C. With decreasing content of retained austenite and ductility, the number of quasicleavage facets increased from ADI grade 1–5. It was also found that fracture morphology of ADI did not experience significant changes when the testing temperature decreased. Evaluation of the bending angle was used to support impact-testing data. Designers and users of ADI castings may use the data developed in this research as a reference.     

High-Temperature Deformation Behavior of Ti-6Al-4V Alloy without and with Hydrogenation Content of 0.27 wt.%

Isothermal compression of Ti-6Al-4V alloy without and with hydrogenation content of 0.27 wt.% was carried out on Gleeble-1500D thermal simulation machine at deformation temperature between 760 and 1000 °C and strain rate from 0.001 to 1 s⁻¹. The experimental results show that hydrogenation can decrease the deformation temperature or increase the strain rate of Ti-6Al-4V alloy. The apparent activation energy was determined to be 667 kJ mol⁻¹ for isothermal compression of the Ti-6Al-4V alloy without hydrogenation content of 0.27 wt.% in the α + β phase region (760-960 °C), and this value was about 655 and 199 kJ mol⁻¹ for the alloy with 0.27 wt.% of hydrogenation content in the α + β phase region (760-840 °C) and β phase region (840-960 °C), respectively. Constitutive equation was developed for the high-temperature deformation of Ti-6Al-4V alloy both without and with hydrogenation content of 0.27 wt.%.     

Interfacial energy of solid bismuth in equilibrium with Bi−In eutectic liquid at 109.5 °C equilibrating temperature

The interfacial energy of solid bismuth (Bi) in equilibrium with Bi−In eutectic liquid was determined for the equilibrating temperature of 109.5 °C. A radial temperature gradient on the sample was established by heating it from the center with a single heating wire and cooling the outside of the sample at −10 °C with a heating/refrigerating circulating bath containing an aqueous ethylene glycol solution. The equilibrated grain boundary groove shapes of solid Bi in equilibrium with Bi In eutectic liquid (Bi- 47.3 at. %In) were observed from a sample quenched at 109.5 °C. The Gibbs-Thomson coefficient and the solid-liquid interfacial energy of the solid Bi in equilibrium with Bi In eutectic liquid were determined to be (8.4±0.4) × 10⁻⁸ K m and (54.0±5.4)×10⁻³ J m⁻² from the observed grain boundary groove shapes. The grain boundary energy of the solid Bi phase was calculated to be (105.5±11.6)×10⁻³ J m⁻² by considering a force balance at the grain boundary grooves. The thermal conductivities of Bi-47.3 at. %In eutectic liquid phase and the solid Bi-47.3 at. %In phase and their ratio at 109.5 °C were measured with a radial heat flow apparatus and a Bridgman type growth apparatus.     

High temperature deformation behavior of Ti−6Al−4V alloy with and equiaxed microstructure: a neural networks analysis

The hot deformation behavior of Ti−6Al−4V alloy with an equiaxed microstructure was investigated by means of Artificial Neural Networks (ANN). The flow stress data for the ANN model training was obtained from compression tests performed on a thermo-mechanical simulator over a wide range of temperature (from 700°C to 1100°C) with strain rates of 0.0001 s⁻¹ to 100 s⁻¹ and true strains of 0.1 to 0.6. It was found that the trained neural network could reliably predict flow stress for unseen data. Workability was evaluated by means of processing maps with respect to strain, strain rate, and temperature. Processing maps were constructed at different strains by utilizing the flow stress predicted by the model at finer intervals of strain rates and temperatures. The specimen failures at various instances were predicted and confirmed by experiments. The results establish that artificial neural networks can be effectively used for generating a more reliable processing map for industrial applications. A graphical user interface was designed for ease of use of the model.     

Beta phase superplasticity in titanium alloys by boron modification

Addition of boron to titanium alloys produces fine TiB whiskers in situ with excellent thermal stability and good chemical compatibility with the matrix. These whiskers stabilize a fine-grain microstructure by restricting grain growth at high temperatures in the β phase field. The hot deformation behavior in the β phase field (temperature range 1050–1200 °C) of Ti-6Al-4V alloys modified with two different levels of B additions (1.6 and 2.9 wt.%) produced by powder metallurgy was investigated using hot compression tests in the strain rate range of 10⁻³ to 10⁻¹ s⁻¹ and hot tensile tests at a nominal strain rate of 6×10⁻⁴ s⁻¹. The β phase exhibits superplasticity, which occurs due to stabilization of a fine-grain microstructure by the TiB. Matrix grain boundary sliding and β/TiB interface sliding appear to contribute to the β superplasticity. The ability to achieve superplasticity at higher temperatures enable lower flow stresses, improved chemical homogeneity, and high strain rate capability due to enhanced accommodation processes. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Deformation mechanism temperature-dependence of AZ31 magnesium alloy

The deformation behavior of AZ31 Mg alloy is studied here in relation to the temperature. A rolled plate with a thickness of 50 mm was first homogenized at 400 °C for 4 h before preparing test specimens with the tensile axis parallel to the rolling direction (RD). A series of tensile tests was then carried out at a strain rate of 10⁻²/s together with load relaxation tests to obtain flow curves in terms of the stress and strain rate at room temperature (RT), 100 °C, 200 °C, and 300 °C. The flow curves were found to represent the usual grain matrix deformation (GMD) behavior, consisting of the accumulation and relaxation of glide dislocations at temperatures of less than 100 °C. At temperatures greater than 200 °C, grain boundary sliding (GBS) was found to play an important role, as described in theories related to an internal variable. The GBS could be characterized as a non-Newtonian viscous flow with a power index value of M _g = 0.5.     

Control of microwave dielectric properties in 0.42ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>−0.58TiO<Subscript>2</Subscript> ceramics by the quantitative analysis of phase transition

Phase constitutions of ZnNb₂O₆−TiO₂ mixture ceramics were significantly changed according to the sintering temperature. Phase transition procedures and their effect on the microwave dielectric properties of 0.42ZnNb₂O₆−0.58TiO₂ were investigated using X-ray powder diffraction and a network analyzer. The fractions of the phases composing the mixture were calculated by measuring integral intensities of each reflection. The structural transitions in 0.42ZnNb₂O₆−0.58TiO₂ were interpreted as the association of two distinct steps: the columbite and rutile to ixiolite transition present at lower temperatures (900–950°C) and the ixiolite to rutile transition at higher temperatures (1150–1300°C). These transitions caused considerable variation of microwave dielectric properties. Importantly, τ_f was modified to around 0 ppm/°C in two sintering conditions (at 925°C for 2 hr and at 1300°C for 2 hr), by the control of phase constitution.     

Continuous dynamic recrystallization of AISI 430 ferritic stainless steel

The high-temperature deformation behavior of AISI 430 ferritic stainless steel was studied by torsion tests. The deformation tests were performed in the temperature range of 900–1100°C and strain rate range of 5.0×10⁻² −5.0/sec. The evolutions of flow stress and microstructure show the characteristics of continuous dynamic recrystallization (CDRX). The flow stress gradually decreased with strain over the peak stress without steady state. Below the 100% effective strain, grains appeared in small angle grain boundaries with a misorientation of 3–9°. In addition, when heavy deformation (>300%) was applied, higher misorientation (∼15°) was achieved. The tendency of CDRX increased with increasing strain rate and decreasing temperature. The dependence of CDRX grain size on the strain rate and temperature was discussed.     

Indirect evaluation of the long-term oxidation properties of Al−21Ti−23Cr and Al−37Ti−12Cr coating materials for TiAl alloy

The most pertinent coating materials in the Al−Ti−Cr alloy system to improve the high temperature oxidation resistance of a TiAl alloy, with respect to oxidation properties, resistance to thermal stress, and chemical compatibility, are the two-phase alloys of Al−21Ti−23Cr (L1₂+Cr₂Al) and Al−37Ti−12Cr (γ+TiAlCr). In this study, cyclic oxidation tests at 1000 °C and 1200 °C were performed for the specimens coated with both materials of 10 im thickness. Furthermore, breakaway oxidation caused by the formation of a rutile TiO₂ scale was observed, though both bulk alloys showed very stable oxidation behavior. This phenomenon was resulted from the depleted Al content in the coating layer due to Al₂O₃ oxide growth and interdiffusion with the substrate. Considering the decrease of Al content due to oxide growth, the Al−21Ti−23Cr coating with the initial higher Al content was more effective for long-term oxidation protection of the TiAl alloy. On the other hand, when the Al content changes due to the interdiffusion with the substrate, the Al−37Ti−12Cr coating with a smaller compositional gradient with the TiAl substrate was more effective than the Al−21Ti−23Cr coating. Cyclic oxidation tests at 1000 °C and 1200 °C confirmed that for the longer lifetime of coating materials the initial Al content was more important than the smaller compositional gradient with the substrate. Consequently, the Al−21Ti−23Cr coating was considered as more effective one for the long-term oxidation resistance of TiAl alloys.