Papers by Keyword: Al Alloy

Abstract: In this study, the 2024 Al powder with different weight fractions of graphite is mechanically milled using a high-energy ball mill for 3 hours each in the nitrogen environment. The milled powder is compacted at an elevated temperature. X-ray diffraction is used to phase analysis of milled powder as well as compacted specimens. Optical microscopy is used for microstructural analysis and hardness measurements are done for the evaluation of mechanical properties. The hot compacted specimens are also tested for their wear properties. Results show that there is no new phase formed during mechanical milling. But, after hot compaction of the milled powder, Al₂Cu formed due to precipitation. No reaction is observed between the aluminum and the carbon (graphite) after milling as well as hot compaction. Microstructures of all hot compacted specimens are not showing pores, which, signifies full density after compaction. The formation of Al₄C₃ is not observed at any stage of processing. Therefore, graphite is uniformly distributed in all specimens, and the same is observed at grain boundaries of α-Al grains in the microstructures. Hardness increases with the addition of 1 wt.% graphite but it decreases with a further increase in graphite. The wear resistance of 2024 Al with 1 wt% graphite is the highest among all the compositions. The high hardness and wear resistance of 2024Al with 1 wt% graphite is the consequence of precipitation of Al₂Cu during hot compaction and the presence of graphite which creates hindrances in the metal matrix. The presence of free graphite in the vicinity of grain boundaries acts as a solid lubricant which improves wear resistance of 2024 Al.

Abstract: The fatigue life of 7050 Al alloy samples after different surface treatments, i.e., as-machined, anodizing, shot peening, and shot peening followed by anodizing, had been tested. The shot peening treatment specimens presented the longest average fatigue life. The fatigue life of anodizing treatment specimens decreased by 69.3% and 78.8% at 215 MPa and 260 MPa stress levels than as-machined ones. Introducing the shot peening treatment before anodizing can increase the fatigue life by 220% / 296.9% at 215 MPa/260 Mpa than that only treated by anodizing. The effect of the surface treatments on the fatigue life were studied by performing surface morphology investigation, residual stress measurements and fracture surface analysis.

Abstract: Interface reaction between SKD61 and three Al melts at 973 K was investigated in this study. In pure Al and A380 alloy, soldering occurred on the samples. Pure Al showed two separated soldering areas consisting of Fe-Al based intermetallic phases, mainly FeAl₃. A380 alloy indicated the expanded soldering area consisting of Al₃Fe and two AlFeSi based intermetallic phases. Al-10mass%Mg alloy showed the absence of soldering, but a formation of a few Fe-Al intermetallic phases. This would be attributed to weakened interaction between Fe and Al caused by Mg enrichment. Microstructures near soldering of pure Al and A380 also showed the precipitations considered as Al₃Fe and AlFeSi intermetallic compounds, respectively. However, in Al-10mass%Mg alloy, there is only intermetallic compound including Mg, V and Ca without Al₃Fe.

Abstract: Oxide scale behaviors by surface segregation of Mg, Ca and Be in Al and their effects on oxidation resistance at melt temperature were investigated. With the addition of Ca and Be in Al-7.5mass%Mg alloy, the samples showed a suppressed weight gain. However, in the initial oxidation, Ca added samples exhibited improved oxidation resistance. As a result of oxide layer observation by microscopy, Ca added Al-7.5mass%Mg alloy exhibited the region overlapped by constituent elements, indicating multi-element oxide is formed on the surface. In the oxidation of Al-Mg-Be system, BeO is formed as primary oxide and mixed layer with MgO, while Ca addition in Al-Mg system causes no change in the primary and secondary oxides, but formation of CaMg₂Al₁₆O₂₇. BeO and BeAl₂O₄ may contribute to balanced layer by combination between constituent oxides in the Al-Mg-Be system. In the case of Ca addition, CaMg₂Al₁₆O₂₇ acts as a filler of the cracks in MgO layer.

Abstract: In the present work, the effect of Cr and Mn addition on corrosion resistance was investigated on AlSi3Mg alloy. Potentiondynamic corrosion tests in a 3.5 wt. % NaCl solution were performed on samples in different heat-treated conditions, and corrosion current density and potential were determined by Tafel method. Brinnel hardness measurements were also carried out in order to couple corrosion resistance with mechanical properties. It was interestingly found that Cr presence enhanced mechanical properties and corrosion resistance in comparison with the base alloy.

Abstract: The repair welding of aluminium alloy 6082T6 with two fillers 4043 and 5356 were studied by using MIG welding process with pulse current at frequency 5 Hz. After that, macrostructure and microstructure were investigated and the density of porosity and testing of mechanical properties were determined. The results found that the density of new weld was less than repair weld. The results of mechanical tests showed that the new weld were better than the repair weld.

Abstract: The effects of solution heat treatment of Al6Si2Cu aluminum alloy on incipient melting of θ-Al₂Cu phase have been investigated. Solution heat treatments, in this study, are applied to improve of mechanical properties through a single-step solution heat treatment. The microstructure of as-cast specimen represents a typical dendrite structure having a secondary dendrite arm spacing of 37um. In addition to the Al matrix, a large amount of coarsen eutectic Si, θ-Al₂Cu intermetallic phases and Fe-rich phases are identified. As the solution temperature increases, the Vickers's hardness increases up to 510°C and thereafter hardness decreases at the temperature of 520°C and 530°C. This hardness behavior may closely related with microstructural evolution such as solubility of alloying elements up to 510°C and also melting of θ-Al₂Cu intermetallic phases over 510°C in this study. Consequentially, the optimal single-step solution heat treatment temperature should be 510°C to improve mechanical property.

Abstract: This paper investigated the effects of two-step solution heat treatment of aluminum alloy for lightweight automotive on mechanical properties. Solution heat treatments in this study are applied to improve of mechanical properties through a single-step and two-step solution heat treatment. The microstructure of AlSiCu casting specimen represents a typical dendrite structure having a secondary dendrite arm spacing (SDAS) of 40 um. In addition to the Al matrix, a large amount of coarsen eutectic Si, Al₂Cu intermetallic phases and Fe-rich phases are identified. After solution heat treatment, the mechanical properties of two-step solution heat treatment alloy show higher values than as-cast and a single-step solution specimens. Consequentially, the two-step solution heat treatment could be used in automotive parts to improve mechanical properties.

Abstract: The influences of spinning deformation and heat treatment on microstructure and tensile properties of A356 alloy at different cooling rates were investigated in this study by optical and scanning electron microscopes. The results indicated that spinning deformation enhanced the tensile properties of the alloy due to the reduction of Si size and porosity percentage, especially in the samples with coarse microstructure. Heat treatment increased the strength while decreased the ductility of the alloy because of the precipitation of brittle Mg₂Si in Al matrix. It is suggested that the spinning deformation processing is an effective technique to produce A356 alloy wheels with high mechanical properties.

Abstract: PVD hard coating is a well-known surface treatment technology for steels to improve wear resistance and, to some extent, corrosion resistance. In principle, hard coating can be carried out for Al alloys, but due to the natural oxide layer and the insufficient load-bearing capacity of the soft base material, the application of this technology for wear protection of components is not regarded as being particularly promising. The research activities described in this paper focused on electron beam (EB) surface alloying with a Co-based additive, and the influence of two different hardness levels (270HV0.1 and 390HV0.1) on the improvement of the local load-bearing capacity of Al alloys with thin PVD hard coatings. A further focus of this research was on the material-specific aspects of the coating deposition. Compared to steels, the hard coated surface of Al alloys is rougher and the measured adhesion of the coating is significantly lower. For this purpose, different technological PVD parameters (e.g. Ti interlayer, deposition temperature, and time) were adapted to optimize the coating properties – especially adhesion. The paper deals with comparative studies of single (PVD hard coating of Al base material) and duplex treatment (EB alloying of Al base material and subsequent PVD hard coating) by means of improvement of the coating and compound hardness, friction and wear behavior (pin-on-disc test), as well as the corrosion resistance (potentiodynamic measurements in 0.05M H₂SO₄). While the level of improvement in wear resistance as a result of the duplex treatments strongly depended on the adhesion of the thin coatings, the corrosion behavior was strongly influenced by the PVD deposition process and coating thickness.