Precipitation Of Mg2Si Research Articles

Influence of Solute Addition in the Microstructure and Hardness of the Al-Si-Cu Alloys

ABSTRACTCommercial aluminum alloys corresponding to Al-Cu-Si family are commonly used in casting and molding process because their high castability. The main characteristics of these alloys are the excellent weight/strength relation in conjunction with wear and corrosion resistance. Additionally, the mechanical properties of these alloys could be enhanced by heat treatment.In Al A319 alloys, Cu and Mg are the main responsible to increase the mechanical properties after T6 heat treatment due to the precipitation of Al2Cu and Mg2Si and Al2CuMg phase [1]. Combined effects of Ni and Cu improve strength and hardness at relatively elevated temperature [2], Due to the low solubility of Ni in Al (0.04%), it has been reported the formation of FeAl9FeNi-type intermetallic, which is not totally dissolved with the typical solution treatments used in aluminum alloys [3]. Hayajneh et al., found that increasing amounts of intermetallic compounds Al3Ni, Al3(CuNi)2 and Al7Cu4Ni in Al-Cu alloy, the hardness increase [4].The effect of Ni addition and solution treatment time on the microstructure and hardness of the Al A319 alloy are studied by Vickers microhardness (VHN), Rockwell B hardness (HRB), X Ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy (SEM).

Metallographic investigation of tensile- and impact-tested aluminum composites

The present work was performed on two composites: Al-15 vol.% B4C and experimental 6063/15% B4C. Additions of 0.45% Ti + 0.25% Zr were made to both composites melts. The composites were cast from the respective melts at 730℃ using two metallic molds to produce tensile as well as impact test samples. All samples were solution heat treated for 24 h at 540℃ for both composites, followed by aging at 200℃ for 10 h. Samples for microstructure and fractography were examined using field emission scanning electron microscopy. The results show that the powder injection technique used in this study produces composites with B4C uniformly distributed throughout the matrix. The strength and impact toughness of the two composites are controlled by the simultaneous precipitation of Al3Zr and Mg2Si phase particles depending on the matrix type. Hardening caused by precipitation of Mg2Si is more pronounced than that caused by Al3Zr phase precipitation. No B4C particle debonding was observed due to the presence of Zr-/Ti-rich layers surrounding the B4C particles. The cracks mainly propagate through the B4C reinforcement particles.

Role of modification and melt thermal treatment processes on the microstructure and tensile properties of Al–Si alloys

Abstract The present study was performed on an Al–7%Si–0.35%Mg alloy (A356 alloy) with the primary objective of improving the alloy performance through modification of the microstructure. Ultimate tensile strength (UTS) can be improved by the addition of strontium (Sr), superheating or Sr modified melt thermal treatment. The melt thermal treatment process alone has no apparent influence on the UTS. Both Sr-modified and Sr-modified melt thermal treatment can help to improve the percentage elongation of A356 alloy castings. A higher percentage elongation can be reached at a higher cooling rate. The effect of solution heat treatment on the tensile properties of various A356.2 alloy castings can be summed up as follows: (i) the yield strength of the A356.2 castings is significantly improved after 8 h solution heat treatment due to the precipitation of Mg2Si, (ii) the yield strength remains more or less the same with further increase in solution treatment time to 80 h, and (iii) the UTS is greatly improved within the first 8 h of solution heat treatment and continues up to 80 h, where this improvement is attributed to Mg2Si precipitation, dissolution of silicon within the Al-matrix and change in the Si particle morphology (spheroidization). The ductility of the A356.2 alloys can also be considerably enhanced with solution heat treatment (e.g. from ∼6% in the non-modified casting in the as-cast condition to ∼10% after 80 h solution treatment).

Influence of TiB2 Addition on the Precipitation Kinetics in Al-7Si-0.3Mg In Situ TiB2 Composites

Precipitation behavior of the Al-7Si-0.3Mg/TiB2in situ composites was investigated using differential scanning calorimetry and transmission electron microscopy, and it was found that Si precipitation is accelerated with increase in TiB2 content. Non-isothermal kinetic analysis clearly showed a decrease in the precipitation kinetics of the overaged metastable precipitates in the Mg2Si precipitation sequence.

Mechanical Properties and Microstructure of Primary and Secondary AA6063 Aluminum Alloy after Extrusion and T5 Heat Treatment

The mechanical properties of primary and secondary AA6063 aluminum alloy were investigated in tension on samples with different orientation (extrusion direction, ED and transverse direction, TD), after quenching in forced air and after artificial aging (T5) at 185°C for 6h. The microstructure of the samples was analyzed using both light optical microscopy and scanning electron microscopy on the surface of the extrudate. The strength values after artificial aging are higher than the strength after quenching in forced air due to the precipitation hardening. The tensile properties show a slight anisotropy between ED and TD. The optical microscopy investigation carried out on the extruded billet after forced air quenching shows a fully recrystallized equiaxed grains. Artificial aging improves the strength and hardness due to the precipitation of Mg2Si observed by scanning electron microscopy (SEM).

The sequence of intermetallic formation and solidification pathway of an Al–13Mg–7Si–2Cu in-situ composite

The phase transformation sequence and solidification behaviour of an Al–13Mg–7Si–2Cu in-situ composite was examined using a combination of computer-aided cooling curve thermal analysis and interrupted quenching techniques. Five different phases were identified by analysing the derivative cooling curves, the X-ray diffraction profile, optical and scanning electron microscopy images and the corresponding energy dispersive spectroscopy. It has been found that the solidification of this alloy begins with primary Mg2Si precipitation and continues with the formation of eutectic Al–Mg2Si, followed by Al5FeSi and simultaneous precipitation of Al5Cu2Mg8Si6 and Al2Cu complex intermetallic phases. The formation of the last three intermetallic compounds changes the solidification behaviour of these composites remarkably due to their complex eutectic formation reactions. The solidification of the alloy, calculated using the Factsage thermochemical analysis software, has demonstrated a good agreement with the experiments in terms of compound prediction, their weight fractions and reaction temperatures.

Dynamic precipitation of Mg2Si induced by temperature and strain during hot extrusion and its impact on microstructure and mechanical properties of near eutectic Al–Si–Mg–V alloy

Dynamic precipitation of Mg2Si and its impact on the microstructures and mechanical properties of Al–12.5wt% Si–0.6wt% Mg–0.1wt% V alloy were studied by applying different extrusion temperatures and extrusion ratios. Optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) observations were used to characterize the microstructure evolution. Tensile properties and the Brinell hardness were tested. Results show that both decreasing extrusion temperature (temperature-induced) and increasing extrusion ratio (strain-induced) of the alloy will result in dynamic precipitation of Mg2Si particles. Dynamic precipitation of Mg2Si leads to a considerable coarsening of the recrystallized grains. Yield strength (YS) and ultimate tensile strength (UTS) of the sample extruded at lower temperature (400°C) are more than 50% lower than that extruded at higher temperature (540°C) with the same extrusion ratio of 16. With increasing of extrusion ratio from 16 to 50, both YS and UTS of the samples decrease nearly 30% when extruded at the same temperature of 540°C.

Microstructural and mechanical behavior of multi-walled carbon nanotubes reinforced Al–Mg–Si alloy composites in aging treatment

Microstructural and mechanical behavior of heat treatable Al–Mg–Si (6XXX series) alloy composites reinforced with multi-wall carbon nanotubes (MWCNTs) fabricated by powder metallurgy process were investigated by SEM-EDS, XRD, tensile test and Vicker’s hardness test. As-extruded P/M 6063 alloy composites with CNT reinforcements indicated a small increment of mechanical strength compared to the monolithic 6063 alloy with no CNT before T6 heat treatment. When T6 heat treatment was applied to the specimens, the 6063 composite with CNTs showed a noticeable decrease of yield stress (YS) improvement, compared to the monolithic Al alloy. It means that Mg2Si precipitates hardening effect by the artificial aging treatment was insufficient for the composite containing CNTs. This was mainly because Mg alloying elements were diffused around CNTs and consumed to form Al2MgC2 compounds, and resulted in the incomplete matrix strengthening behavior by Mg2Si precipitation after the aging treatment.

Experimental Correlation for the Effect of Metallurgical Parameters on the Hardness of 356 and 319 Aluminum Alloys Using Minitab Software

The present study was undertaken to investigate the effect of metallurgical parameters on the hardness and microstructural characterisations of as-cast and heat-treated 356 and 319 alloys, with the aim of adjusting these parameters to produce castings of suitable hardness and Fe-intermetallic volume fractions for subsequent use in studies relating to the machinability of these alloys. Hardness measurements were carried out on specimens prepared from 356 and 319 alloys in the as-cast and heat-treated conditions, using different combinations of grain refining, Sr-modification, and alloying additions. Aging treatments were carried out at 155 °C, 180 °C, 200 °C, and 220 °C for 4 h, followed by air cooling, as well as at 180 °C and 220 °C for 2, 4, 6, and 8 h. Peak hardness was observed in 356 alloys when aging was carried out at 180oC/4h. In the case of unmodified or modified 356 alloys containing mostly α-Fe intermetallics, aging at 180 °C up to 8h produced a sharp rise in hardness during the first two hours of aging, followed by a broad peak or plateau over the 2-8 h aging period. Aging at 220 °C revealed a hardness peak at 2h aging time for both 356 and 319 alloys. Addition of Mg to unmodified or modified 319 alloys produced a remarkable increase in hardness at all aging temperatures. This may be explained on the basis of the combined effect of Cu-and Mg-intermetallics in the 319 alloys, where hardening during aging occurs by the cooperative precipitation of Al2Cu and Mg2Si phase particles.[, ] For 356 and 384 alloys, the Mg-containing 319 alloys (~same Mg concentration as in 356 alloys) displayed higher hardness values than the 356 alloys for the aged condition, where hardening occurs by cooperative precipitation of Al2Cu and Mg2Si phase particles in 319 alloys compared to only Mg2Si precipitation in the case of 356 alloys.

Microstructural Analysis of Laser Coated Ceramic Components TiB2 and TiC on Aluminium Alloy EN AW-6082-T651

This paper deals with the deposition of ceramic powder coating TiB2-TiC mix with aluminium powder on the 6082-T651 aluminium alloy by means of laser coating. The resulting coating was studied by means of a microstructural and microchemical analysis. Microhardness was measured in the coating and in the substrate area under the coating. A thermodynamic analysis of the system showed the potential existence of aluminium carbide Al4C3 in the coating, whereas the EDS analysis indicated a possible occurrence of aluminium oxycarbides in the coating, containing TiB2, TiC and Al. An additional thermal analysis explained the existence of two separate exothermic peaks, on the basis of which it could be inferred that the precipitation of phase Mg2Si, which is a typical precipitate in aluminium alloy 6082, occurred. Microhardness measurements confirmed the differences in the hardness of the coating, resulting from different energy input during the coating process. Due to the thermal effect of the coating process and the rapid cooling of the coating and the coating-substrate interface, microstructural changes occurred on the substrate surface under the coating. The modified microstructure under the coating resulted in reduced hardness, which could be attributed to the use of the alloys in the precipitation-hardened state. Thermal effects of the coating process and rapid cooling contributed to the occurrence of forced dissolution with reduced microhardness.

The effects of rolling parameters on the mechanical behavior of 6061 aluminum alloy

The present work has been conducted to study the effect of rolling parameters (strain rate and temperature) on the microstructural evolutions and mechanical properties of 6061 aluminum alloy. The results indicate that the predominant restoration process during rolling at 250°C is dynamic recovery, and the driving force is not high enough to trigger dynamic recrystallization. However, primary recrystallized grains were clearly evident in the microstructure of the specimen rolled at 350°C. Moreover, at 450°C not only the volume fraction of dynamically recrystallized grains is increased but the formation of some new precipitates is recognized. The tensile test results show that the room temperature strength and ductility are increased by increasing the rolling temperature in the range of 250–450°C. Moreover, at a given rolling temperature the yield strength is decreased with increasing strain rate. The observed trends are explained through microstructural evolutions upon hot rolling as well as dynamic precipitation of Mg2Si and the Fe or Cu rich particles.

Optimization of homogenization for a low alloyed AlMgSi alloy

Abstract The homogenization practice for EN AW 6060 was investigated. It takes an 8-hour soak at 580 °C to level out the Mg and Si distribution in the matrix and to transform the monoclinic β-Al5FeSi plates into relatively small α-AlFeSi particles. The solute Si and Mg are largely retained in solution during subsequent cooling at > 500 °C h− 1. Mg2Si precipitation is considerable, however, during cooling at

High Temperature Mechanical Properties of Al–Si–Mg–(Cu) Alloys for Automotive Cylinder Heads

To improve the fuel efficiency and reduce automobile emissions, there has been growing demand of more durable alloys for engine components with the improved thermal and fatigue resistance. This study examined the effect of alloying elements on the high mechanical behavior of Al–Si–Mg–(Cu) casting alloys for cylinder heads. Depending on the alloying elements affecting the strength of the matrix, the thermal expansion coefficient decreased with increasing Mn and Cu content at high temperatures with a concomitant increase in the elastic modulus, hardness and tensile strength. Quantatative analysis showed that the mechanical properties of the Al2Cu precipitate hardened alloy were maintained at temperatures over 250°C, whereas the degradation of mechanical properties of the Mg containing alloy occurred at 170°C due to coarsening of the Mg2Si precipitation phase. The LCF (low cycle fatigue) lives decreased with increasing alloy content according to the Coffin-Manson relation due to the smaller elongation. On the other hand, an analysis of the fatigue lives with the hysteresis loop energy, which consists of both strength and elongation, showed that the fatigue lives were normalized with an alloy of the same strengthening mechanisms regardless of the test temperature.

Effect of Duplex Ageing on the Properties of A356 Alloy Containing Rare Earth Elements

Reduced weight of automobiles for the purpose of fuel economy has encouraged the use of light metals especially aluminium alloys. A356 Al alloy containing 7% Si and 0.3% Mg is widely used in automobile and aircraft industries due to excellent castability, good corrosion resistance and good pressure tightness. A356 is age hardenable alloy and there is appreciable improvement in strength and hardness achievable due to precipitation of intermetallic compound Mg2Si. In the present investigation, aluminium alloy A356 with and without rare earth (RE) addition (0.5 wt%) was subjected to single ageing as well as double aging treatment. The results were compared for mechanical properties like hardness and ultimate tensile strength with the material not containing RE additions.

Effect of Artificial Aging (T6) on Microstructure of Al-AC8H/Al<sub>2</sub>O<sub>3</sub> MMC Produced by Stir Casting Route

The purpose of this research is to systematically study the influence of artificial aging (T6) on evaluation of microstructure changed and hardness of Al-Al2O3 composite produced by stir casting route. The Al2O3 particle reinforced previously was coated by electroless coating method to improve wetting system between Al-AC8H and Al2O3 when aluminium composites fabricated by stir casting route. The volume fraction of Al2O3 which added into Al melts was various from 2% to 22.5%. The stirring process was carried out at 500-700 rpm to achieve vortex in alumnium melt using graphite impeller for 15 minutes. The prepared aluminium composites then heat treated by T6 treatment with different aging time. Microstructure and hardness after T6 treatment were investigated. It was observed that microstructure changed after T6 while hardness increase after T6 due to the Mg2Si precipitation hardening was present in Al matrix as well as Si eutectic accumulated on the surface of Al2O3. It was found that the optimum hardness occurred after aging for 3 hours.

The microstructure and mechanical strength of Al-6061-T6 GMA welds obtained with the modified indirect electric arc joint

Plates of Al-6061-T6 with a thickness of 12.7 mm were welded with a non-heat treatable ER4043 electrode in four welding passes using the typical single V groove butt joint (at room temperature) and in one pass using the novel modified indirect electric arc (MIEA) joint (at 50, 100 and 150 °C). Microstructural characterization of the weld metal revealed that the MIEA joint design yielded microstructures in which columnar growth was restricted and a grain refining effect occurred without the addition of inoculants, even with preheating of the joints. The self-refining effect in the MIEA joint was discussed in terms of the cooling behavior and the large dilution of base material. Vickers microhardness profiles revealed that the high dilution rates obtained with the MIEA joint caused alloying of the weld pool with magnesium producing a weld metal composition sensible to heat treating due to the precipitation of Mg 2Si precipitates. The grain self-refining effect of the MIEA joint along with alloying of the weld metal were found to have a profound impact on the mechanical properties of the welded joints.

A new etching technique for revealing the plastic deformation zone in an Al–Cu–Mg alloy

A new etching technique for revealing the plastic deformation zone in an Al–Cu–Mg alloy has been developed. The etching with the proposed etching agent was conducted on the deformed sample after being heated to 673 K for 3 h. With this etching technique, the plastic deformation zone was clearly observed even under low magnification. This was due to the change of microstructural characteristics in the plastic deformation zone after the heating process, in which there is significant precipitation of Al2Cu and Mg2Si, caused by the high energy arising from the severe deformation.

Corrosion behavior of Al–60 vol.% SiC p composites in NaCl solution

In this study, corrosion behavior of pure Al and Al–4 wt.% Mg alloy matrix composites, comprising 60 vol.% SiC particles, has been investigated. Composites were produced by pressure infiltration technique at 750 °C. The corrosion tests were carried out in 3.5 wt.% NaCl environment up to 28 days. The weight loss of the composites increased with increasing duration time up to 3–5 days then remained constant. Scanning electron microscopy (SEM) analysis showed that Al–4 wt.% Mg alloyed matrix composite exhibited higher corrosion resistance than pure Al matrix composite although potentiodynamic polarisation measurements showed higher i corr values of Al–4 wt.% Mg alloyed matrix composites than pure Al matrix composites. Experimental results revealed that precipitation of Mg 2Si as a result of reaction between Al–Mg alloy and SiC particle has a beneficial effect on corrosion resistance of Al–4Mg alloy matrix composites due to interruption of the continuity of the matrix channels within the pressure infiltrated composites.

Advanced light metals casting development: solidification of aluminium alloy A356

Microstructural reactions during solidification of aluminium alloy A356 were analysed using cooling curve analysis to determine the evolution in fraction of solid. The experiments involved recording the temperature/time data under different cooling rates so that the various phase changes associated with solidification could be identified in both unmodified and strontium modified versions of the alloy. Once collected, the cooling curve data were processed to calculate the first derivative together with a baseline cooling curve (cooling curve in the absence of any transformations). Comparison of the baseline cooling curve with the first derivative data allowed accurate identification of start temperatures of the various liquid to solid transformations and characterisation of fraction solidified during the cooling process. Strontium modification altered the morphology of A356, decreased the precipitation temperature of new phases (2°C to 11°C), and increased the solid fraction of the beginning of eutectic and Mg2Si precipitation (0.01 to 0.05). Cooling rate appeared to have no effect on solid fraction evolution but an increase in cooling rate reduced solidus temperature (48°C to 75°C).

In Situ observations of the evolution of precipitates on the surface of Al-6022

The precipitation of Mg2Si on the surface of Al 6022 has been investigated in situ using a Confocal Scanning Laser Microscope and a gold image furnace during cooling and isothermal conditions. It was found that precipitates form during cooling at temperatures between 400 and 280°C. The numbers and size of precipitates, as well as the growth velocity have been obtained as function of temperature for different cooling rates. The growth of precipitates has been modeled by means of a normalized Gaussian function, which can be used to predict the precipitate evolution.