Development of Al-Mn-Mg 3004 alloy for applications at elevated temperature via dispersoid strengthening

In this study, the potential applications of Al-Mn-Mg 3004 alloy at elevated temperature have been evaluated through the systematic study of the precipitation behavior of α-Al(MnFe)Si dispersoids and their effect on material properties during precipitation treatment and long-term thermal holding. The results demonstrate a significant dispersion strengthening effect caused by the precipitation of fine uniformly distributed dispersoids during precipitation treatment. The peak compression yield strength (YS) at 300°C of the experimental 3004 alloy can reach as high as 78 MPa due to a large volume fraction (~2.95 vol. %) of α-Al(MnFe)Si dispersoids. The dispersoids are found to be thermally stable at 300°C for up to 1000 h of holding, leading to consistently high mechanical performance and creep resistance. The superior and stable YS and creep resistance at 300°C enables the 3004 alloy to be applied to weight-sensitive applications at elevated temperatures

Tensile deformation behavior of Al-Cu 206 cast alloys near the solidus temperature

To study the micromechanics of semisolid deformation, a modified experimental set-up is employed in Gleeble 3800 thermomechamical testing unit to achieve a uniform temperature distribution in partially remelted aluminum samples. The temperature variation was markedly reduced to one degree for a length of 4-5 mm in the middle of tensile samples. High temperature semisolid tensile tests of Al-Cu 206 cast alloys were performed at different temperatures near solidus with a strain rate of 10-3 s-1, corresponding to the solid fractions (fs) between 1 and 0.95. The stress-displacement curves with different fs were measured and analyzed. The microstructure and fracture surface of samples were examined by optical and scanning electron microscopes. The relation between the microstructural characteristics, tensile properties and fracture behavior of semisolid 206 samples at high fs were explored. Mush deformation mechanisms were discussed in term of defect nucleation and propagation at the late stage of solidification

Transient Rheological Behavior of Semisolid SEED-Processed 7075 Aluminum Alloys in Rapid Compression

© 2018, The Author(s). The transient rheological behavior and microstructure evolution of semisolid SEED-processed 7075 aluminum alloys were studied using the rapid compression tests. The effects of the TiB2 grain refinement on the grain morphology and size of semisolid slurries were investigated. Results indicated that the grain refiner could reduce the grain size and improve the globularity of α-Al grains. The grain-refined alloy can be easily deformed at a wide range of solid contents (0.42 to 0.53 Fs), in which the deformation level appears to be independent from the solid content. Under the transient state, the apparent viscosity decreased with increasing shear rate to a minimum value and followed by an increase as the shear rate decreased. The apparent viscosity of the base alloy exhibited a dependency on the solid content, while the apparent viscosity of the grain-refined alloy in the decreasing or increasing shear rate periods was not substantially influenced by the solid content. The viscosity as a function of applied shear rate can be described using the power law viscosity model. The differences in the flow behavior index (n) and the consistency index (k) for two alloys were discussed

Precipitation behavior of dispersoids and elevated-temperature properties in Al–Si–Mg foundry alloy with Mo addition

In the present work, Mo was added to an Al-Si-Mg foundry alloy to study its influence on the evolution of dispersoids during various heat treatments. The microhardness as well as the elevated-temperature tensile properties and creep resistance was measured to evaluate the contribution of dispersoids. Results showed that the addition of Mo greatly promoted the formation of α-dispersoids. During solution treatment, the formation of α-dispersoids started after 8 hours at 500 °C. At high temperature (540 °C), the coarsening of dispersoids with increasing time became predominant. The optimum condition of dispersoids can be reached by 520°C/12h or 500°C/4h + 540°C/2h, leading to the highest differences in microhardness between the Mo-containing alloy and base alloy. The tensile strengths were improved at both room temperature and elevated temperatures, while the elongation at elevated temperature was greatly increased. The creep resistance at elevated temperature is further enhanced due to the Mo addition

Microstructural evolution and dynamic softening mechanisms of Al-Zn-Mg-Cu alloy during hot compressive deformation

The hot deformation behavior and microstructural evolution of an Al-Zn-Mg-Cu (7150) alloy was studied during hot compression at various temperatures (300 to 450 °C) and strain rates (0.001 to 10 s−1). A decline ratio map of flow stresses was proposed and divided into five deformation domains, in which the flow stress behavior was correlated with different microstructures and dynamic softening mechanisms. The results reveal that the dynamic recovery is the sole softening mechanism at temperatures of 300 to 400 °C with various strain rates and at temperatures of 400 to 450 °C with strain rates between 1 and 10 s−1. The level of dynamic recovery increases with increasing temperature and with decreasing strain rate. At the high deformation temperature of 450 °C with strain rates of 0.001 to 0.1 s−1, a partially recrystallized microstructure was observed, and the dynamic recrystallization (DRX) provided an alternative softening mechanism. Two kinds of DRX might operate at the high temperature, in which discontinuous dynamic recrystallization was involved at higher strain rates and continuous dynamic recrystallization was implied at lower strain rates

Enhanced elevated-temperature properties via Mo addition in Al-Mn-Mg 3004 alloy

The present work investigates the influence of adding Mo to an Al-Mn-Mg 3004 alloy on elevated-temperature properties as well as their thermal stability during long-term thermal holding at 350°C and 400°C. In as-cast and heat-treated conditions, both microhardness and yield strength increase with increasing Mo contents and reach peak values at 0.3 wt. % followed by a plateau. With an optimized Mo content (0.3 wt. %), the volume fraction of dispersoids is increased while the volume percentage of the dispersoid-free zone is greatly reduced compared to the base alloy free of Mo, resulting in the remarkable increases in elevated-temperature strength and creep resistance. The results of the long-term thermal holding show that compared with the rapid drop of elevated-temperature strength and creep resistance in the base alloy, the Al-Mn-Mg alloy with 0.3% Mo is thermally stable up to 350°C, exhibiting a slight decrease of stability at 400°C. The combination of high elevated-temperature properties and their excellent thermal stability at 350-400°C with Mo addition makes Al-Mn-Mg 3xxx alloys the promising candidates for elevated-temperature applications

Fabrication of Superhydrophobic Surfaces on Aluminum Alloy Via Electrodeposition of Copper Followed by Electrochemical Modification

Superhydrophobic aluminum surfaces have been prepared by means of electrodeposition of copper on aluminum surfaces, followed by electrochemical modification using stearic acid organic molecules. Scanning electron microscopy (SEM) images show that the electrodeposited copper films follow "island growth mode" in the form of microdots and their number densities increase with the rise of the negative deposition potentials. At an electrodeposition potential of -0.2 V the number density of the copper microdots are found to be 4.5x10^4 cm-2 that are increased to 2.9x10^5 cm-2 at a potential of -0.8 V. Systematically, the distances between the microdots are found to be reduced from 26.6 μm to 11.03 μm with the increase of negative electrochemical potential from -0.2 V to -0.8 V. X-ray diffraction (XRD) analyses have confirmed the formation of copper stearate on the stearic acid modified copper films. The roughness of the stearic acid modified electrodeposited copper films is found to increase with the increase in the density of the copper microdots. A critical copper deposition potential of -0.6 V in conjunction with the stearic acid modification provides a surface roughness of 6.2 μm with a water contact angle of 157◦, resulting in superhydrophobic properties on the aluminum substrates­

Fabrication of corrosion resistance micro-nanostructured superhydrophobic anodized aluminum in a one-step electrodeposition process

The formation of low surface energy hybrid organic-inorganic micro-nanostructured zinc stearate electrodeposit transformed the anodic aluminum oxide (AAO) surface to superhydrophobic, having a water contact angle of 160°. The corrosion current densities of the anodized and aluminum alloy surfaces are found to be 200 and 400 nA/cm2, respectively. In comparison, superhydrophobic anodic aluminum oxide (SHAAO) shows a much lower value of 88 nA/cm2. Similarly, the charge transfer resistance, Rct, measured by electrochemical impedance spectroscopy shows that the SHAAO substrate was found to be 200-times larger than the as-received aluminum alloy substrate. These results proved that the superhydrophobic surfaces created on the anodized surface significantly improved the corrosion resistance property of the aluminum alloy

Corrosion resistance properties of superhydrophobic copper surfaces fabricated by one-step electrochemical modification process

Superhydrophobic copper surfaces have been prepared by a one-step electrochemical modification process in an ethanolic stearic acid solution. In this work, the corrosion properties of hydrophobic copper surface and superhydrophobic copper surfaces were analyzed by means of electrochemical analyses and compared with that of as-received bare copper substrate. The decrease of corrosion current density (icorr) as well as the increase of polarization resistance (Rp) obtained from potentiodynamic polarization curves revealed that the superhydrophobic film on the copper surfaces improved the corrosion resistance performance of the copper substrate

Fatigue cycles and performance evaluation of accelerating aging heat treated aluminum semi solid materials designed for automotive dynamic components

The A357-type (Al-Si-Mg) aluminum semi solid casting materials are known for their excellent strength and good ductility, which make them materials of choice, preferable in the manufacturing of automotive dynamic mechanical components. Semi-solid casting is considered as an effective technique for the manufacturing of automotive mechanical dynamic components of superior quality performance and efficiency. The lower control arm in an automotive suspension system is the significant mechanical dynamic component responsible for linking the wheels of the vehicle to the chassis. A new trend is to manufacture this part from A357 aluminum alloy due to its lightweight, high specific strength, and better corrosion resistance than steel. This study proposes different designs of a suspension control arm developed, concerning its strength to weight ratio. Furthermore, this study aims to investigate the effect of accelerating thermal aging treatments on the fatigue life of bending fatigue specimens manufactured from alloy A357 using the Rheocasting semi-solid technology. The results revealed that the multiple aging cycles, of WC3, indicated superior fatigue life compared to standard thermal aging cycles. On the other hand, the proposed designs of automotive suspension control components showed higher strength-to-weight ratios, better stress distribution, and lower Von-Mises stresses compared to conventional designs