Materials Science Forum Vols. 546-549

Abstract: Electronic tensile testing, scanning electron microscope, transmission electron microscope, X-ray diffractometer and high resolution transmission microscope were employed to investigate the mechanical properties, microstructure, tensile fracture and morphology of the precipitated phases of an electrolytic low-titanium wrought 6009 aluminum alloy. Results showed that the mechanical properties of the electrolytic aluminum sheet were improved by solid solution treatment incorporating with pre-aging treatment. The tensile strength and extensibility were enhanced by a factor of 23% and 38% by pre-aging treatment at 150 °C for 5 minutes respectively; a large quantity of nucleation sites of β˝ phase were generated by pre-aging treatment, which was propitious to the transformation from solid solution state to GP zone, and the stable size of GP zone formed during the pre-aging process promoted the precipitation of Mg2Si phase. The Mg2Si phase was revealed by HRTEM and the crystalline stripes were obtained by Fourier transformation.

Abstract: The effect of 0.30 Yb (mass fraction,%) additions on the microstructure and properties of high strength Al-Zn-Mg-Cu-Zr aluminum alloys has been investigated by TEM, optical microscopy, hardness and electric conductivity measurement, tensile test, stress corrosion cracking test. The results show that the ytterbium additions to high strength Al-Zn-Mg-Cu-Zr aluminum alloys significantly inhibited recrystallization during solution treatment. The tensile and yield strengths, elongation, hardness, electric conductivity and stress corrosion cracking resistance of the Yb-containing alloys are improved compared to the alloys without Yb additions. By Yb additions, the critical stress intensity (KISCC) is enhanced from 7 MPa·m1/2 up to 14.5 MPa·m1/2 with the improvement of the strength and ductility. The mechanism for the property improvement from Yb additions has been discussed.

Abstract: A procedure of thermo-mechanical treatment (TMT) was carried out to 2519 aluminum alloy to improve its properties. The influences of cold deformation ratio, ageing temperature and ageing time of the TMT on the mechanical properties and electrochemical corrosion resistance of this alloy were investigated. The results show that after TMT the tensile strength of 2519 aluminum alloy can be improved obviously but its electrochemical corrosion resistance decreases slightly. The optimum processing parameters of the TMT for 2519 aluminum alloy can be described as: solid solution at 530°Cfor 0.5h, then cold deform with a ratio of 15% followed by aging at 150°C for 10h.

Abstract: Deformation microstructures and micro-orientations of columnar grains with different orientations in a polycrystalline high purity Al cold-rolled up to 65% (thickness reduction) were investigated using electron backscatter diffraction (EBSD) technique. It was found that rotations were Inhomogeneous within the individual grains, the rotation angles of the parts close to the initial boundaries (BPs) were smaller than those remote from the boundaries (IPs), e.g. the deviation angles between the BPs and the IPs were 5-6° in the grains with <001>//RD orientation, leading to the rotation along the α-fiber, while the deviation angles were 5-12° in the grains with <121>//ND orientation rotating toward the β-fiber. These results demonstrated that the microstructures and local rotations of various parts within the rolled individual columnar grains were influenced by their initial orientations and boundaries.

Abstract: The kinds, morphologies and distributions, enclosed the micro-structural evolvement of Al-1.5Si-1.1Mg-0.5Cu alloy during homogenization treatment were investigated by means of optical microscopy, XRD, SEM/EDS and TEM/EDS. The results show that there were mainly three kinds of morphologically distinct constituents in as-cast Al-1.5Si-1.1Mg-0.5Cu alloy for automotive panels, such as coarse Mg2Si and Al8(FeMn)2Si, and multiphase eutectic structure consisted of AlMgSiFeCu elements, except the α-Al matrix phase. The coarse Mg2Si and Al8(FeMn)2Si were distributed in the α-Al interdentritic regions or at grain boundaries, the former sometimes appears more obvious eutectic characteristics than the later one. The multiphase eutectic products distributed both inside grains with agglomerate aspects and along the α-Al interdentritic regions or at grain boundaries, which is contained with Si and Al2Cu. Coarse binary eutectic structure Mg2Si partly dissolved into matrix and the eutectic characteristics disappeared, whereas Al8(FeMn)2Si changed a little during homogenization. Agglomerate multi-eutectic structures were non-equilibrium products, some of them fully dissolved into matrix and the others partially dissolved and left the discrete blocky Si behind after homogenization.

Abstract: Metallurgical quality of roll casting sheet is crucial to ensure the performance of aluminum foil. An electromagnetic purification system was installed in a twin roll casting line in order to improve the molten metal cleanliness. Metallographic analysis shows that inclusion particles larger than 10 μm can be eliminated from molten aluminum by electromagnetic purification and a total inclusion removal efficiency of 75% is achieved additional to the filtration by a ceramic foam filter. The electromagnetic purification system operated reliably and consistently during the casting campaign.

Abstract: 2519A aluminum plate was shot obliquely by an incendiary projectile with the diameter of 7.62mm at impact velocity of 818m/s. The penetration inhomogeneities of the crater of 2519A aluminum target plate were investigated with optical microscopy (OM), scanning electron microscopy (SEM). Melted substance, a mixture of the target material and the projectile was found at the interface of target and projectile. Different microstructural characteristics were observed along the crater depth. Grains were elongated near the entrance area, while severely kinked grains and adiabatic shear bands were present in the middle region, and microbands, as well as abnormal grown grains, appeared at the crater bottom. The failure form of target is mainly ductile expanding.

Abstract: When Al-Ni alloys solidified from melted zone and semi-solid zone, respectively, with a magnetic field up to 12.0T (Tesla) applied, the paramagnetic Al3Ni crystals in the precipitated Al3Ni phase were aligned with their c-axes parallel to the field and a unique laminated textured microstructure of the precipitated phase perpendicular to the field was formed. There were critical values of magnetic intensity Bcrit and heating temperature Tcrit at or above which the textured microstructure could be formed. The behavior of magnetic orientation of the precipitated phase was investigated experimentally. The results were discussed in terms of magnetic rotation of crystals with magnetic anisotropy, crystal growth, mechanical and magnetic interactions among the magnetized Al3Ni grains in a high magnetic field.

Abstract: The dynamic recrystallization characteristic of 3104 alloy has been investigated by isothermal compression deformation at temperatures from 573K to 773K under constant strain rates ranges from 10-3s-1 to 1s-1. It was shown that the form of flow stress curves were very sensitive to temperature and strain rate. At high temperatures and low strain rates, dynamic recrystallization of 3104 alloy deformation occured. The critical value for dynamic recrystallization start was determined from an inflection point that was observed in the plot of work hardening rate vs. flow stress and verified metallograhically based on quenching samples interrupted during deformation. In the experimental domain studied, the ratio of the critical strain for the initiation of dynamic recrystallization to that of the peak strain falled in the range 0.4-0.6. Furthermore, the dependence of εc on Zener-Hollomon parameter( Z) has been developed.

Abstract: The plastic deformation behaviors of 7050 Al alloy were investigated by compression tests at temperatures ranging of 250°C
450°C under constant strain rates of 0.01s−1, 1s−1 and 10s−1. The results showed that all the flow curves consisted of three stages, i.e. strain-hardening, strain-softening and steady state-strain. Initially, the stress rises steeply at microstrain deformation, and then increases at a decreased rate, followed by a strain-softening until a steady state stress. The stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon parameter in an exponent-type equation, 1 19 7.202 σ p 80.71 sinh (1.64 10 Z) = ⋅ −  × − ⋅ −  . Elongated grains with serrations developed in the grain boundaries were observed; the dynamic recrystallization (DRX) occurs with increasing temperature and dislocation density, and the shape of grain at steady state is nearly equiaxial. It can be concluded that the DRX phenomenon is sensitive to the temperature and the dynamic flow softening is mainly as the result of dynamic recovery and DRX.