xMg Alloys Research Articles

Influence of Mg Content on the Corrosion Behavior and Precipitation of Aged Al-Cu-Li-xMg Alloys

Aluminum (Al)–copper (Cu)–lithium (Li) alloys are susceptible to environmental degradation, which limits the in-service lifetime of the components. Because of their complex composition, there are seldom studies focusing on corrosion behavior influenced by one single element, which is essential to clarify the corrosion mechanism. Herein, the sole influence of Mg on the corrosion behavior of Al–Cu–Li–xMg alloys was analyzed. Results revealed that the addition of Mg can affect the nucleation and precipitation process of the T1 precipitate, resulting in a difference of potential between grain interior and grain boundary. The precipitation of the T1 precipitate was promoted in a 0.7Mg alloy while impeded in a 1.1Mg alloy, due to the competition of Cu atoms and nucleation sites between T1 and S′. Two types of corrosion behavior of Al–Cu–Li–xMg alloys appeared due to the potential difference and continuity of grain boundaries. Continuous precipitates in grain boundaries and less precipitates within the grain are likely to cause intergranular corrosion (IGC), while more precipitates within the grain will result in pitting.

Performance of an Al–0.08Sn–0.08Ga–xMg alloy as an anode for Al–air batteries in alkaline electrolytes

Aluminum (Al) electrodes doped with metals, such as Sn, Ga, and Mg, were prepared by smelting to study the effects of Mg content on the properties of Al electrodes. After testing the corrosion resistance and electrochemical properties (in 4 M NaOH solution) of the Al–0.08Sn–0.08Ga–xMg alloy, the results were compared to virgin Al and an Al–Sn–Ga alloy. The battery performance was studied by constant current discharge. Scanning electron microscope and energy-dispersive X-ray analysis were used to investigate the corrosion form and discharge surface of the alloys. Results showed that the Mg–Sn and Mg–Ga phases act as corrosion centers enabling negative corrosion potential. Electrochemical test results revealed that compared with the pure Al and Al–Sn–Ga alloy, the Al–0.08Sn–0.08Ga–0.5Mg alloy not only showed a more negative potential but also showed enhanced activity. Moreover, it showed high energy density (3169.7 Wh kg−1) and improved anode efficiency (86.9 ± 0.2%) when used as an anode for an aluminum–air battery in NaOH solution.

Structural Properties Evaluation of Semisolid Extruded Al–Cu–Mg Powder Metallurgy Alloys

Structural properties evaluation of semisolid extruded Al–4Cu–xMg alloy preforms have been performed in the present investigation. Pressureless sintering of Al–4 wt% Cu with varying Mg (0, 0.25, 0.5, 0.75 and 1 wt%) powder mixture was performed in an inert atmosphere. The sintering behavior and mechanical properties of all alloys were investigated at different temperatures and compositions, respectively. The maximum density and hardness (647 MPa) were found in the Al–4Cu–0.5 Mg composition sintered at 550 °C. Semisolid extrusion was carried out on sintered Al–4Cu–0.5 Mg alloys having an Initial Relative Density of 80% and 90% to find the structure–property correlation due to deformation. Extrusion was carried out in between solidus (542.7 °C) and liquidus (662.8 °C) temperatures with different solid fractions, which were derived from the TG/DTA analysis. All experiments were performed with low extrusion ratio of 1.44, strain rate of 0.1 s−1 and die approach angle of 30°. Structure–property correlation study of extruded rod was performed at front end, middle part and rear end to understand the temperature and metal flow profiles during deformation process. There were no visible defects found in the demarcated samples. The presence of Al2Cu precipitate in the extruded alloy was identified by X-Ray diffractometer and scanning electron microscope with energy dispersive spectroscopy analysis. The microstructural evolution was observed in all the extruded bars by optical microscope. Micro-hardness of extruded samples was found to be 1001 MPa, which was almost two times of sintered sample.

Microstructure, mechanical and thermo-physical properties of Al–50Si–xMg alloys

There is a growing demand to achieve better performance of electronic packaging materials owing to the development of modern electronics industry. In this work, the effects of elemental Mg addition on microstructural characteristics, mechanical properties, and thermo-physical properties of Al–50Si alloys were investigated. The tensile strength, bending strength, and hardness are improved significantly when the Mg content increases from 0% to 1%, but decreases as the content exceeds 1%. The enhanced strength is mainly attributed to the presence of small bar-like Mg2Si phase located at the interface. However, the extensive growth of Si phase in the high Mg contained alloys reduce the mechanical properties. The thermal conductivity and thermal expansion coefficient decrease gradually with the increase in the Mg content. Compared with the addition of Cu, minor amount of Mg addition (0.5%) can effectively increase the strength of Al–50Si alloys without substantially sacrificing the thermal conductivity.

Role of Mg in simultaneously improving the strength and ductility of Al–Mg alloys

We found that when Mg is added to Al in small amounts, it results in alloys that exhibit both significantly higher strength and ductility than those of the pure Al counterpart. Strength and plasticity are contrasting properties for most crystalline alloys; as such, the simultaneous improvement of these properties seems contradictory from the viewpoint of dislocation motion. Comparative studies of Al–xMg alloys containing different amounts of Mg were performed to elucidate how these apparently mutually exclusive properties were improved simultaneously; microstructural observations were made using X-ray diffractometry and transmission electron microscopy to assess the effect of Mg on the strength and ductility on the alloys, while molecular dynamics simulations were performed to comprehensively understand how the resulting high-strength alloys could also exhibit high ductility.

Influence of Mg Contents on Aging Precipitation Behavior of Al–3.5Cu–xMg Alloy

The influence of Mg content on the microstructures and mechanical properties at room temperatures of Al–3.5Cu–(0.71–1.81)Mg alloys was studied. Precipitation phases in the alloys were identified by TEM and HRTEM. The results show that when Mg contents increase from 0.71 to 1.81 wt%, the precipitates are transformed from S, S″, Ω, and θ′ phases to S and S″ phases, and Ω phase is first observed in Al–3.48Cu–0.71 Mg alloy with Cu/Mg mass ratio of 5 during the conventional aging heat treatment (190 °C/12 h). Regard to aging hardness effect of the tested alloys, the hardness of the alloys improves with the increase of Mg content, but the increases become slow when Mg content is greater than 1.35 wt%.

Effect of high magnesium content on microstructure of Al–7Si alloy

A new class of ternary Al–7Si–xMg alloys was developed with improved microstructure consisting of fine spheroidal Mg2Si and eutectic Si particles dispersed in α-Al. The studies show that Mg and Sr have a modification effect on eutectic Si and Mg2Si particles respectively. In alloys with high Mg, a combination of Sr addition followed by T6 treatment resulted in a fine and spheroidal eutectic mixture of Si and Mg2Si. It was concluded that 2wt% Mg is optimum to obtain a minimum amount of coarse Mg2Si particles in the Al–7Si–xMg system as well as modify the eutectic Si particles. Furthermore, the hardness of Al–7Si–xMg alloys with and without Sr addition is comparable with those of in-situ Al–7Si–TiB2 composites indicating that they can be used as an alternative for the composites for wear resistant applications.

Microstructure and mechanical properties of Al–xMg alloys processed by room temperature ECAP

Abstract Microstructure development and mechanical properties of Al–xMg alloys (x = 0, 1, 5–10 wt%), processed by ECAP at room temperature, have been investigated. The results show that the microstructures of Al–xMg alloys are refined by the interaction of shear bands and their increase in number during ECAP. The addition of magnesium to aluminum promotes the grain refinement. Misorientation increase induced by particles along grain boundaries is observed by using high resolution EBSD. As ECAP strain increases up to 4, the strength of Al–6 wt% Mg alloy increases progressively while the elongation decreases from 31.7% to 5.5%. A good combination of both strength and ductility has been obtained by annealed ECAP. The change in softening mechanism of the Al–6 wt% Mg alloy, processed by 6 passes of annealed ECAP, occurs in the range of 523–573 K.

Characterisation of intermetallic particles formed during solution treatment of an Al–7Si–0.4Mg–0.12Fe alloy

When Fe-containing Al–7Si–xMg alloys are solution-treated, usually as the initial stage of a T6 heat treatment, some of the π-Al9Mg3FeSi5 phase present in the as-cast alloy transforms into fine needle-like intermetallic particles (as seen on a polished surface). These precipitated needles, speculated to be β-Al5FeSi phase, have not been definitively characterised to date. In this work, electron microscopy characterisation by various techniques was conducted to assess the nature (i.e. the composition, morphology and crystallography) of these particles to verify or otherwise the validity of the above hypothesis. It is found that the particles are indeed β phase platelets, of the same Al5FeSi or Al4.5FeSi stoichiometry as particles formed during solidification. Close observation of their crystallographic structure suggests fine-scale internal complexities in some of the particles.

Mechanical and wear behaviors of Al–12Si– XMg composites reinforced with in situ Mg 2Si particles

A study has been conducted to investigate the mechanical and wear behaviors of the Al–12Si– XMg alloys (where Mg contents were 5%, 10% and 20%) cast by adding modifiers such as Sr, red phosphorous and salt mixtures. Mechanical properties were determined by hardness measurements, compression and wear tests. Reciprocating wear tests were conducted by rubbing ceramic (Al 2O 3) and steel (AISI 52100) balls on the unlubricated surfaces by applying the normal load of 2 N. The microstructure of the Al–12Si– XMg alloys consisted of the Si needles and Mg 2Si precipitates (two morphologies of which are polyhedral shape dark particles and grey colored components of Chinese script) in the Al matrix. Results demonstrated that volume fraction and size of the primary Mg 2Si particles increased with increasing the Mg content. Mg containing alloys exhibited higher hardness and better wear resistance than the Mg free alloy.

Production and corrosion behaviours of the Al–12Si– XMg alloys containing in situ Mg 2Si particles

In this study the mechanical behaviours of Al–12Si– XMg alloys (where Mg contents varied up to 20%) have been investigated. The alloys were prepared by casting followed by extrusion at 300 °C with a ratio of 1.6. Precipitation of the Mg 2Si phases was observed in the Mg containing Al–12Si alloys as two different morphologies; i.e., as a polyhedral primary particle and as a Chinese script. Results showed that volume fraction and size of the primary Mg 2Si particles increased with increasing the Mg content. Mg containing alloys exhibited higher hardness, compression strength and lower corrosion resistance than the Mg free alloy.

Wear and corrosion behaviours of extruded Al–12Si– XMg alloys

In this study mechanical and corrosion behaviours of Al–12Si– XMg alloys (where Mg contents varied up to 20%) have been investigated. The alloys were prepared by casting followed by extrusion at 300 °C with a ratio of 1.6. Precipitation of the Mg 2Si phases was observed in the Mg containing Al–12Si alloy matrix with two different morphologies; i.e. as a polyhedral primary particle and as a Chinese script. The amount and size of the primary Mg 2Si particles increased with increasing the Mg content, which was accompanied by an improvement in hardness and wear resistance but a reduction in corrosion resistance.

Microstructural characteristics and mechanical properties of Al–2.5 wt.% Li–1.2 wt.% Cu– xMg alloys

Microhardness of heat-treated Al–2.5 wt.% Li–1.2 wt.% Cu–0.12 wt.% Zr– xMg alloys was observed to increase with increasing Mg content mainly due to increased solid solution strengthening, reduced grain size and increased amount of fine quasi-crystalline Al 6Cu(Li, Mg) 3 precipitates. Although coarse quasi-crystalline Al 6Cu(Li, Mg) 3 phases were found in all investigated alloys, the quasi-crystalline phase as a fine precipitate could be only observed in the alloys containing high Mg contents. The tensile strength was significantly increased in the alloys with high Mg contents after a heat treatment, owing to the enhanced precipitations of fine Al 3Li and Al 3Zr phases.

TEM microstructural characterization of melt-spun aged Al–6Si–3Cu– xMg alloys

Three Al–6Si–3Cu– xMg alloys ( x = 0.59, 3.80 and 6.78 wt.%) were produced using melt-spinning. As-melt-spun ribbons were aged at 150, 180 and 210 °C for times between 0.05 and 100 h. Microstructural changes were examined using transmission electron microscopy (TEM) and microhardness was measured. TEM analysis of the as-melt-spun alloys revealed 5 nm nanoparticles and larger particles (50 nm) composed of Al 2Cu ( θ) for the 0.59% Mg alloy and Al 5Cu 2Mg 8Si 6 (Q) for 3.80% and 6.78% Mg alloys. Silicon solid solubility was extended to 9.0 at.% and Mg in solid solution reached 6.7 at.%. After aging treatments the 6.78% Mg alloy exhibited the most significant increase in microhardness, reaching 260 kg/mm 2. TEM analysis of aged specimens also showed θ and Q phase (5–20 nm nanoparticles and 35–40 nm particles). The combination of the volume fraction and size of the particles plays an important role in microhardness variation.

Synthesis and characterization of mechanical-alloyed Ti– xMg alloys

The synthesis and characterization of Ti– xMg ( x=4, 9, 12, 15, 21, 24 at%) alloys using mechanical alloying was investigated. A nanometer-sized Ti–24Mg alloy was produced. During mechanical alloying, the height of the XRD peaks of the Mg in the Ti–9Mg alloy decreased, and then disappeared, whereas the Ti XRD peaks broadened, and the grain size decreased with increasing milling time. The Mg firstly dissolved in the grain boundaries of the Ti, and then diffused into the Ti grain interiors. The grain boundaries played an important role in enhancing the solid solubility of Mg in Ti. With increasing Mg content the volume fraction of grain boundaries increased, and a decrease in grain size occurred after mechanical alloying for 48 h.