Materials Science Forum Vols. 638-642

Abstract: The effect of PFZ and grain boundary precipitates formed in aging processes on the macroscopic mechanical properties in Al-Zn-Mg(-Ag) alloys were evaluated using TEM, SEM, tensile test and nanoindentation. Decreases in width of PFZ and smaller size of grain boundary precipitates aging at lower temperatures and/or the addition of Ag processes improved the tensile properties, and the presence of PFZ was found to be harmful to the fracture. Nanoindentation hardness results clarified that the hardness within PFZ is smaller than that in grain interiors, indicating that, in the alloy with large width of PFZ, preferential deformation occurs within PFZ in the initial stage of deformation, and this causes lower elongation regardless of the same level of proof stress and the same sizes of grain boundary precipitates. From the quantitative correlation between precipitate microstructures in the vicinity of grain boundaries, mechanical properties and fracture morphologies, the deformation process of the alloys is considered to divided by three types; i.e. in case of the alloys with the small width of PFZ and the small size of grain boundary precipitates, in case of the alloys with the large width of PFZ and the small size of grain boundary precipitates and in case of the alloys with the large width of PFZ and the large size of grain boundary precipitates.

Abstract: Adaptive Neural Networks (ANN) can be used in the analysis of a complex panorama of interconnected input/output industrial data, even when they present substantial noise. The ANN, despite presenting substantial mathematical complexity associated with non-linear parameterization (which includes transfer equations and corresponding “training”), are largely used under industrial conditions in several engineering areas (such as in steelmaking), with substantial success. This work shows the applicability of the ANN in a specific case related to the analysis of internal defects of extruded aluminum sections (occurring both at the head and at the extrusion tail), and the associated bar hardness as a function of process parameters such as: billet temperature, extrusion ratio, ram speed and billet length. Results were analyzed in terms of the adhesion to an ANN built upon the collected industrial data, as well as the relevance of each variable within the ANN.

Abstract: In the present study, microstructure evolution of Ti-Fe alloys with different Fe content between 0.2-1.5mass% during hot deformation in (α+β) two-phase region is studied with focusing on effect of phase volume fraction at different deformation temperatures and strain rates. Hot deformation was conducted on the specimens quenched after β solutionizing at 1173K for 1.2ks at 1108, 1073 and 948K, by uniaxial compression by 50% at various strain rates ranged from 1 to 10-4 s-1. Initial structures are (α+β) lamellar structures of fine interlamellar spacing and colony sizes. Increase in Fe content results in increasing the fraction of the β phase at the given deformation temperature. Either colony size or interlamellar spacing is coarser at higher temperatures. At the higher deformation temperature where β phase fraction is larger, dynamic recovery of β phase is a major deformation mechanism while at a lower temperature, i.e., a higher α fraction, dynamic recrystallization of α phase occurs predominantly. It is concluded that critical strain needed for occurrence of dynamic recrystallization is decreased by increasing fraction of the α phase at the same deformation temperature, i.e., by decreasing Fe content. Furthermore, by increasing strain rate grain size of the recrystallized α is decreased.

Abstract: Aluminium is increasingly used in structural components in cars. The advantages are many, and recyclability, weight saving and energy absorption during impact and are often considered as the most important. There are also several disadvantages compared to iron and steel, i.e. material cost, low stiffness, lack of fatigue limit, high thermal conductivity, high thermal expansion coefficient, corrosion susceptibility and others. To enhance the advantages and to minimize the disadvantages, several actions can be made. To prevent recrystallization is one of them, and has to be dealt with from the melt through all thermo-mechanical, mass reducing and assembly processes – “from the ore to the car”. As recrystallization may reduce the static strength and fatigue life time in a finished component considerably, preventing recrystallization is as important as to optimize component geometry. Additionally, there is considerable risk of inter-granular cracking or melting during thermo-mechanical processing, especially those involving very high strain and forming temperatures above eutectics. To prevent recrystallization, a well balanced budget on chemical composition, strain, strain rates and temperatures is essential. Examples of successes and failures are vital ingredients of the base of knowledge in development of highly utilized aluminium car components. All process steps, from alloying and melt treatment of wrought aluminium alloys to the assembly of a finished component, can influence on product performance. AlMgSi1 alloys are used as examples in evaluating recrystallization in this paper. By focusing on recrystallization, other major factors influencing performance are not neglected, but not further discussed here.

Abstract: The effects of strain, annealing time and temperature during the processing of an Al-Sn-based triboalloy were researched by response surface analysis. A second-degree polynomial in strain-time-temperature space was compared to a formulation based on generally accepted physical models for recrystallisation, recovery and grain growth, using the rule of mixtures for a microstructure consisting of recovered, recrystallised and second-phase grains. The polynomial approach provides interesting information on the role of rolling reduction in the optimisation of the alloy. The mechanism-based approach yields higher precision with less fitting parameters and provides insight into the relative importance of the physical phenomena involved in the processing of an alloy which has rarely been studied from the viewpoint of physical metallurgy.

Abstract: Dynamic recovery (DRV) and dynamic recrystallization (DRX) play important roles during thermomechanical processes of light metals and alloys because they have obvious influence on microstructure evolution and finally on the mechanical properties of the worked material. Hot compression tests of 7050 aluminum alloy was carried out on Gleeble1500D thermomechanical simulator to modeling multi-pass hot rolling process. Microstructure evolution features of the alloy deformed to a reduction up to 80% were investigated through OM, TEM and EBSD observations. DRX behavior of the alloy during hot compression was emphasized. Some evidence of continuous DRX can be found in the alloy deformed at different temperatures and reductions. The main nucleation mechanisms of DRX are subgrain coalescence and subgrain growth. However, static recrystallization takes place in the material during slow cooling after hot compression.

Abstract: A friction stir weld in 6005A-T6 aluminum alloy has been prepared and analyzed by micro-hardness measurements, tensile testing and scanning electron microscopy (SEM). The locations of the various weld zones were determined by micro-hardness indentation measurements. The flow behavior of the various zones of the weld was extracted using micro-tensile specimens cut out parallel to the welding direction. The measured material properties and weld topology were then introduced in a fully coupled micro-mechanical finite element model, accounting for nucleation and growth of voids as well as void shape evolution. The model shows satisfactory preliminary results in predicting the tensile behaviour of the weld and the true strain at fracture.

Abstract: With an aim of clarifying the strength of rapidly solidified P/M materials strengthened by solid solution of Mg and dispersion of transition metal compounds at elevated temperature, Al-2mass%Mn, Al-4mass%Mn and Al-6mass%Mn alloys with varied Mg additions of 0, 1 and 3 mass% were prepared by rapid solidification techniques. Rapidly solidified (RS) flakes were produced by remelting alloy ingots in a graphite crucible, atomizing the alloy melt and subsequent splat-quenching on a rotating water-cooled copper roll under argon atmosphere.　The RS flakes were consolidated to the P/M materials by hot extrusion after vacuum degassing. Cast ingots of these alloys were also hot-extruded under the same conditions to the I/M as reference materials. Metallographic structures and constituent phases were studied for the P/M and I/M materials by optical microscope and X-ray diffraction. Mechanical properties of as-extruded and annealed P/M materials and as-extruded I/M materials were examined by tensile test at room and elevated temperatures under various strain rates. Uniform dispersion of fine intermetallic compounds (Al6Mn) was observed in all the as-extruded P/M materials. Added Mg was present as the solute in I/M and P/M materials alloy even after annealing. The P/M materials containing Mg exhibited higher hardness and strength at room temperature, than those without Mg. It was considered that both solid solution of Mg and dispersion of intermetallic compounds were contributing the hardness and strength increase in the rapidly solidified Al-Mn-Mg alloys. Tensile strength increases with increasing amount of Mg in I/M materials at all testing temperatures. However, strength of as-extruded P/M materials decreases with addition of Mg at 573K and 673K. Thus the positive effects of Mg additions on tensile strength of as-extruded P/M materials disappeared at higher testing temperature. Tensile strength of annealed P/M materials in which dislocation density decreased and compound particle coarsened increased with addition of Mg at elevated temperatures.

Abstract: An electromagnetic purification system was installed to process molten aluminum in an Al-RE rod continuous casting and hot rolling line. The variation of inclusion concentration in rod samples with and without electromagnetic purification was detected via quantitative metallography. The tensile strength and electrical resistivity of as-rolled rods as well as subsequently cold drawn wires were also tested. Results show that a 61% additional improvement of removal efficiency was achieved by electromagnetic purification other than ceramic foam filtration. The inclusion concentration in the rods has negligible impact on electrical resistivity of samples and the deformation restricts the fluctuation of electrical properties apparently. The UTS of drawn wires with electromagnetic purification improves by 3%-5% as compared with those with filtration only, while the variation of inclusion concentrations has little influence on the UTS of as-rolled rods. A negative linear relationship between the logarithm of UTS and the logarithm of inclusion area fraction for cold-drawn samples is also obtained.

Abstract: Compression and compressive creep behavior was studied on Al-Ti-V ternary alloys containing gamma+beta dual phase microstructures; the gamma phase was based on an L10 face centered tetragonal lattice and the beta phase on a disordered body centered cubic lattice. Yield strength and its temperature dependence have been compared with those in the gamma and/or beta single phase materials. The ternary alloy compositions were located on one assumed conjugate line across the gamma+beta dula phase field: the terminal compositions for the gamma and beta phase constituents were Al51Ti40V9 and Al35Ti20V45, respectively (numbers in atomic %). Three other alloys were prepared that contained different fractions of the constituent gamma and beta phases. The Al47Ti35V18, Al43Ti30V27, and Al39Ti25V36 alloys contained beta phase by about 22, 57, and 76 % in their area fractions. All these alloys showed limited deformability at temperature below 900K. The 0.2% proof stresses of the alloys were described in a similar way as a combination law at the room temperature; the 0.2% proof stress increased from about 500 to 1000 MPa with increasing the vanadium content. The high strength of the alloys containing high level of vanadium retained up to 900K, but the proof stress drastically diminished as the temperature was raised above 900K. Under compressive creep tests performed at temperatures ranging from 1100 to 1200 K, the minimum creep rates were smaller in the alloys containing less vanadium, and this could be ascribed to the fact that the beta phase was much softer than the gamma phase at higher temperatures than about 1000K.