Microstructures and Properties of Extruded Al-0.6Mg-0.6Si Aluminium Alloy for High-speed Vehicle

AbstractThe Al-0.6Mg-0.6Si aluminium alloy was extruded for high-speed vehicle. The microstructure and mechanical property of extruded Al-0.6Mg-0.6Si aluminium alloy were investigated. The results of experimentation show that the tensile strength of extruded Al-0.6Mg-0.6Si aluminum alloy is above of 245MPa, and the percentage elongation after fracture is better than 8%. The microstructure is rolling structure, and the coarse second phases distribute in α-Al solid solution matrix structure. The second phases are inclusions, coarse stable phases of β′ (Mg2Si) or their collection. The tiny β′ (Mg2Si) strengthening precipitation phases mostly distribute in the grain boundary. The size of β′ strengthening phase is about 5nm. The width of no precipitation band is above of 50nm. The fatigue life is 1.061×105 cycle when σmax=0.75σb. The fatigue cracks initiate in surface of extruded Al-0.6Mg-0.6Si aluminium alloy sample. The fatigue fracture is composed of the initiation zone, the propagation zone, and the sudden fracture zone, which is characteristic of a mixed-type fatigue fracture

A Cyclic Calibration Method of Milling Force Coefficients Considering Elastic Tool Deformation

In metal-cutting technology, milling plays an important role in the product development cycle. The accurate modeling and prediction of milling forces have always been research hotspots in this field. The mechanical model based on unit-cutting force coefficients has a high prediction accuracy of cutting forces, and it is therefore widely used in the modeling of milling forces. The calibration of the cutting force coefficients can be realized by linear regression analysis of the measured average milling forces, but it needs to carry out multiple groups of variable feed slot milling experiments with full radial depth of cut, and it cannot well represent the interaction condition in peripheral milling with a non-full radial depth of cut. In peripheral milling, the tool will inevitably deform under the influence of cutting force in the direction perpendicular to the machining surface. If the force-induced deformation is ignored, the calibration of the cutting force coefficients will be out of alignment. For this non-slot milling condition where one side of the tool is mainly stressed, a cyclic calibration method for milling force coefficients considering elastic deformation along the axial contact range is proposed. Firstly, the cutting force coefficients are preliminarily calibrated by the experimental data, and, secondly, tool deformation is calculated through a preliminarily calibrated cutting force model cycle until convergence, before cutting boundaries are updated. The cutting force coefficient is then calibrated again, and it is brought back to the cantilever beam model in order to calculate the tool deformation again. The above process is repeated until the cutting force coefficient is convergent. Finally, the cutting force coefficients are obtained in order to predict and model the milling forces

Multi-ETS carbon prices forecasting based on EMD-SVM model

With the widespread attention of governments around the world on climate issues, carbon pricing-related policies have been gradually adopted by countries to deal with climate change. Among these policy tools, the carbon emissions trading system (ETS) is the most widely used. Carbon price plays a crucial role in this trading system, not only determining the trading activity, but also affecting the market stability. Therefore, carbon price prediction is so significant that we are motivated to study it. However, carbon price presents complex nonlinear dynamic characteristics, which makes some existing methods inaccurate. To address it, this paper combines empirical mode decomposition (EMD) and support vector machine (SVM) to predict carbon prices. The original carbon prices are signal-decomposed by using EMD and the decomposed signal is predicted by using SVM. Based on the EMD-SVM model, this paper conducts empirical analysis on the carbon prices of multi-ETS, including European Union ETS and China ETS pilots. The results of analysis show that the EMD-SVM model has better overall forecasting ability, and carbon prices forecasting performance of China ETS pilots is better than that of the EU ETS, while the short-term forecasting results of the model show the opposite conclusion. The proposed EMD-SVM model is advisable in carbon prices forecasting for market participants and regulatory authorities of multi-ETS

Fatigue Property and Small Crack Propagation Mechanism of MIG Welding Joint of 6005A-T6 Aluminum Alloy

In this study, metal inert gas welding (MIG) was applied to 4 mm thick 6005A-T6 aluminum alloy welding. Compared with other parts, the hardness of the weld zone (WZ) was the lowest, about 67 HV. There was the Softening in WZ, which might make WZ the weakest zone. Then, fatigue tests were carried out on MIG welded joints. All the fatigue specimens fractured at the weld toe of the lap joint, and the fracture was characterized by a cleavage fracture. Crack closure induced by oxide was observed during the steady propagation of the fatigue crack. Impurities hindered crack propagation, changed the direction of crack propagation, and appeared in stepped fatigue strip distribution morphology; in the process of the main crack propagation, the initiation and propagation of small cracks were easily restricted and hindered by the main crack, which slowed down the propagation rate and even stopped the propagation directly

Microstructure and Fatigue Properties of 6061 Aluminum Alloy Laser-MIG Hybrid Welding Joint

Laser-MIG hybrid welding of 6061-T6 aluminum alloy was carried out with ER4043 welding wire, and the microstructure and fatigue properties of the joint were studied. The grain size of HAZ is larger than that of base metal (BM) due to the influence of welding heat cycle. Snowflake-like equiaxed grains were found in the upper, middle, and lower parts of the welded joint (WJ). Based on the fatigue test with 1 × 106 cycles, the ultimate fatigue strength of BM and WJ is 101.9 MPa and 54.4 MPa, respectively. There are many pores with different sizes in WJ. The number of pores in the upper and middle parts of WJ is obviously larger than that in the lower part due to the influence of the cooling rate of the weld pool and the escape rate of pores. The porosity type is mainly metallurgical pores with regular morphology, which is mainly due to the bubbles formed by the evaporation of Mg elements and H2O in the oxide film on the BM surface. The fatigue fracture analysis shows that the main cause of fatigue crack is the near-surface pores with 460 μm and 190 μm, respectively. The existence of pores near the surface is equivalent to the formation of a large-scale prefabricated crack, resulting in serious stress concentration. The morphology of the grains around the pores has a great influence on the initiation and propagation of the fatigue microcracks

Study of Microstructure and Fatigue in Aluminum/Steel Butt Joints Made by CMT Fusion-Brazing Technology

Cold metal transfer (CMT) fusion brazing technology was used to weld 6061 aluminum alloy and Q235 galvanized steel with ER4043 welding wire. The microstructure, hardness, tensile performance, and fatigue performance of the welded joint were observed and analyzed. The results show that the tensile strength of the welded joint is 110.83 MPa and the fatigue strength limit is 170 MPa. In the fatigue process, the coupon first undergoes cyclic hardening and then cyclic softening and a ratchet effect occurs. The coupon was broken at the interface layer or weld zone where the fatigue strength limit is the lowest. The fatigue crack initiation is mainly caused by: (1) inclusions and second-phase particles; and (2) porosity and incomplete fusion. When cracks encounter holes during expansion, the expansion direction will change. The fatigued coupon displays a toughness fracture in the instantaneous fracture zone

Improving the wear resistance of HVOF sprayed WC-Co coatings by adding submicron-sized WC particles at the splats' interfaces

In this paper, the submicron-sized WC particles (similar to 300 nm) with the content of 3 wt% and 5 wt.% are incorporated into high velocity oxy-fuel (HVOF) sprayed WC-Co coatings with the aim of improving properties of the coatings. XRD analyses suggest a small amount of decarburization of the incorporated WC phase after the composite coating deposition. The SEM microstructure showed even distribution of WC particles at the interfaces of WC-Co splats, indicating significantly enhanced wear resistance of the coatings with the wear rate as much as similar to 10(-7) mm(3)/N. m. The content of submicron-sized WC particles plays an important role in determining the wear performances of the coatings. The increment of submicron-sized WC particles causes a decrease in wear rate from 6.09 x 10(-7) mm(3)/N.m to 5.15 x 10(-7) mm(3)/N.m. Also, the Vickers microhardness of the coatings enhances as the increasing of WC particle ratio (reaches 1365 HV with the content of the WC particles of 5 wt.%). The wear failure analysis gives further insight into the mechanism of the property enhancement. The change of stress state and crack initiation at splats' interfaces act as the predominant mechanism, which is caused by the presence of submicron-sized WC particles at splats' interfaces. (C) 2015 Elsevier B.V. All rights reserved

Study on fatigue crack growth of electron beam selective melting of titanium alloy

In the application of additive manufacturing, it is inevitable to use some formed parts with a smaller height. The analysis of various mechanical properties of these formed parts is the focus of research. In this paper, the fatigue performance of a titanium alloy specimen with a 10 mm height and electron beam selective melting is studied. By analyzing the structure and phase of the overall fatigue specimen, and then cutting the overall specimen parallel and perpendicular to the additive manufacturing direction, the tensile and fatigue tests in different directions are performed to detect the fatigue cracks at the fracture propagation the way to research. It is found that there are two ways of secondary crack propagation between fatigue bands, and three cracks are generated during the fatigue secondary crack propagation

Study on Microstructure and Fatigue Damage Mechanism of 6082 Aluminum Alloy T-Type Metal Inert Gas (MIG) Welded Joint

In this experiment, the T-joint of a 6082 aluminum alloy was welded by metal inert gas (MIG) welding and a fatigue test was carried out at room temperature. The mechanisms of generating pores and of fatigue fracture in welded joints are revealed in the case of incomplete penetration. There are two main types of pores: pores that are not welded and pores that are near the upper weld line of the weld. During welding, bubbles in the molten pool are adsorbed on the surface oxide film that is not penetrated, and cannot be floated to form pores; since it is a T-shaped welded joint, the molten pool is overhanged during welding, thereby forming pores near the fusion line. The fatigue strength of the welded joint based on the S–N curve at 107 cycles is estimated to be 37.6 MPa, which can reliably be predicted in engineering applications. Fatigue tests show that fatigue cracks are all generated in the pores of the incomplete penetration, and it and the pores form a long precrack, which leads to large stress concentration, and the fracture occurs under a small applied load. Grain morphology around the pores also has a large effect on the fatigue properties of the T-weld joint. In the weld’s fatigue fracture, it was found that the crack stable-extension zone exhibited ductile-fracture characteristics, and the instantaneous fault zone is composed of a large number of tear-type dimples showing ductile fractures

Microstructure, Fatigue Properties and Stress Concentration Analysis of 6005 Aluminum Alloy MIG Welded Lap Joint

This paper studies the microstructure and mechanical properties of MIG (Melt Inert Gas) lap welded 6005 aluminum alloy plates. Microstructure analysis (OM) of the joint showed that 15~30 μm small grains were observed at the fusion line. Mechanical analysis shows that the small grains are broken by shielding gas and molten pool flow force. Hardness test shows that there is a softening zone (41~43 HV) in HAZ much lower than BM and WZ. The low cycle fatigue test showed that the performance of lap joint decreased sharply, and the fatigue strength of weld decreased significantly, which was only 27.34% of the base metal. The fatigue fracture (SEM) of the weld observed slip band cracking and a large number of brittle fracture characteristics. Using the stress concentration factor Kt for analysis, it was found that the cause of brittle fracture was mostly stress concentration. Lap joint stress concentration model appears in two ways: firstly, at the weld toe, the weld is subjected to eccentric force, secondly, there is a small gap between the two plates at the weld root, which cracks along the direction of 45° of the maximum shear stress