Papers by Keyword: Al-Mg-Si

Abstract: Hybrid composites are gaining increasing interest in the development of aluminium metal matrix (AMCs) for various industrial applications owing to their ability to integrate multiple functionalities within a single material matrix with enhanced physio-mechanical properties as opposed to single-fibre reinforced composites. Green plantain peel ash (GPPA) is an agricultural waste with potential for reinforcement purposes. However, no study has investigated GPPA natural filler as a reinforcement for AMCs. This study, therefore, aims at assessing the influence of variations in GPPA particles and alumina as reinforcements in the fabrication of hybrid composites using Al-Mg-Si alloy as a matrix. This study also reassessed the chemical composition of the GPPA particles and investigated their mechanical properties. However, enhanced mechanical properties, including hardness, tensile strength, and ductility, were observed at varying weight ratios. Results obtained in this study suggest a promising potential application of GPPA particulates as complementing reinforcements in the production of lightweight, strong, and high-performance AMCs well-suited for engineering, aerospace, construction, and packaging applications.

Abstract: The effects of two-stage aging on the microstructures, tensile properties and intergranular corrosion (IGC) sensitivity of Al-Mg-Si alloys were studied by tensile testing and IGC experiments and transmission electron microscope (TEM). The results show that the two-stage aging (180°C, 2h+160°C, 120h) can reduce the IGC sensitivity without decrease the tensile properties. The grain is distributed with high-density β′′ phases, and the grain boundary phases are spherical and intermittently distributed. The formation of the microstructure characteristic is due to the lower re-aging temperature, which results in a decline differences in the diffusion rate between the matrix and grain boundaries. As a result, the pre-precipitated phase can maintain a better strengthening effects due to the slower growth rate. The pre-precipitated phase of the grain boundary presents a spherical and intermittent distribution due to the fast coarsening speed.

Abstract: The effects of Mg/Si ratio on precipitation behaviour and properties of Al-Mg-Si alloys were studied by using electrochemical test, corrosion test and transmission electron microscope (TEM). The results show that with the increases of Mg/Si ratio from 0.9 to 1.1, the density of the β" decreases, and the mechanical properties decrease. When the ratio of Mg/Si increases from 1.0 to 1.1, the density y of β" does not increase significantly, but the continuous degree of the MgSi phase decreases significantly. The source of cracks originate from MgSi phase, which reduces the mechanical properties. When the Mg/Si ratio is 0.9, the alloy is in an over-Si state, which results in serious intergranular corrosion (IGC).

Abstract: The influences of Mg/Si and heat-treatment on the corrosion performance of Al-Mg-Si-Ag alloy were studied. The results show that when the Mg/Si<1, apart from the precipitation of β phase, there is a small amount of elemental silicon. In the corrosion process, the Si element acts as a cathode, which on the one hand leads to the decrease of the corrosion potential, and on the other hand, it increases the corrosion rate. When Si is excessive, the βʺ density increases significantly, and the continuity of the grain boundary phase becomes higher, which promotes electrochemical corrosion, resulting in severe intergranular corrosion (IGC). In under-aging state, the alloy exhibits the best corrosion resistance. The corrosion current density in the slightly over-aged state is slightly lower than that in the peak-aged state. The slightly over-aging treatment can effectively improve corrosion resistance of the alloy. After the alloy treated by severely over-ageing, the grain boundary coarsened and result in the increase of corrosion current density.

Abstract: The effects of welding wire composition on microstructure and mechanical properties of welded joint in Al-Mg-Si alloy were studied by electrochemical test, X-ray diffraction (XRD) analysis and metallographic analysis. The results show that the weld zone is composed of coarse columnar dendrites and fine equated grains. Recrystallized grains are observed in the fusion zone, and the microstructure in the heat affected zone is coarsened by welding heat. The hardness curve of welded joint is like W-shaped, the highest hardness point appears near the fusion zone, and the lowest hardness point is in the heat affected zone. The main second phases of welded joints are: matrix α-Al, Mg₂Si, AlMnSi, elemental Si and SiO₂. The addition of rare earth in welding wire can refine the grain in weld zone obviously, produce fine grain strengthening effect, and improve the electrochemical performance of weld.

Abstract: The aluminum alloy Al–5%Mg–2%Si, the chemical content of which is close to that of the Magsimal-59 aluminum alloy commonly for die casting, was successfully cast into strips using a vertical high-speed twin-roll caster at a speed of 30 m/min. This means that Al–5%Mg–2%Si is suitable for the high-speed twin roll-casting. The as-cast Al–5%Mg–2%Si strip was then successfully cold-rolled to a thickness of 0.7 mm. Tension and cup tests were conducted on the cold-rolled annealed strips. The tensile stress was 205 MPa and the elongation was 20% for a thickness of 1 mm. The limiting drawing ratio was 2.0 at a 0.7 mm thickness. The present results demonstrates that Al–5%Mg–2%Si can be used for die casting and sheet forming. This means that use of this alloy for both sheet forming and die casting could eliminate the need for the separation of wrought aluminum alloys from cast aluminum prior to processing at recycling plants.

Abstract: The precipitation sequence of an Al-Mg-Si alloy depends on many parameters. In this study the natural aging effect on the activation energy of the precipitation sequence in the Al-Mg-Si alloy have been investigated by differential scanning calorimetry (DSC). The precipitation sequence of an Al-Mg-Si alloy has been established. The activation energy of the precipitation process was calculated using Kissinger model. The results obtained using this method showed a change in the activation energy for all precipitated phases. The activation energy of the metastable phases (β″ and β′) and the stable phase β formation in the Al-Mg-Si alloy aged at room temperature have been determined.

Abstract: Al-Mg-Si system alloy have good strength and high ductility without heat treatment. However, the castability in this alloy is inferior to other aluminum alloy, in particular, hot-tearing is easy to occur during solidification. In our previous study, hot-tearing was not occurred in the case of 0.04%Sr addition to this alloy, because of the remarkable refinement of eutectic Mg₂Si phase. In this study, in order to clarify the mechanism of the change of the crystallized eutectic Mg₂Si morphology, the effect of Sr addition on the solidification structure in Al-6%Mg-3%Si alloy was investigated. By Sr addition to this alloy, the change of the nucleation mode from homogeneous to heterogeneous was occurred with the temperature drop at the start of eutectic reaction, and the great change of eutectic growth mode from facet to non-facet was thought to be a main reason improving of hot-tearing.

Abstract: The manufacturing of AA6xxx car body panels typically consists of rolling, ageing and forming processes. Thus, multiple simulation tools can be coupled to set up a through-process modelling (TPM) framework for predicting the evolution of microstructure and the final mechanical properties of these products. In order to realize such a TPM concept, various industrial processing phenomena were studied and modelled in the open innovation research cluster “Advanced Metals and Processes” (AMAP^♯). This work focuses on the age hardening behavior which takes place during the industrial paint bake process. To reflect the microstructure evolution of this processing step, a multi-component precipitation model is developed. So far, the influences of thermomechanical processes, i.e. annealing temperature on the kinetics of Mg_xSi_y precipitates during artificial aging were implemented. The precipitation model was linked to a yield strength model in order to simulate the evolution of mechanical properties within the TPM framework. For validation, the evolution of microstructure and mechanical properties of an AA6016 alloy during artificial ageing was investigated via transmission electron microscopy (TEM) and tensile testing. The simulation results are in agreement with experimental observations.

Abstract: In the structures of all metastable precipitates in Al-Mg-Cu and Al-Mg-Si alloys, we find that column surrounding of an element column in the needle/lath direction order according to simple principles. Advanced transmission electron microscopy and DFT calculations support the principles originate with a line defect, which is a segment of a <100>Al column shifted to interstitial positions. We propose the defect aids solute decomposition by partitioning the FCC matrix locally into columns of fewer and higher number of nearest neighbours, which suit smaller and larger size solute atoms, respectively. The defect explains how <100> directionality of the precipitates can arise in a cluster. Ordering of a few defects leads naturally to GPB zones in Al-Mg-Cu and to β'' in Al-Mg-Si.