Effect of Isothermal Reheating at Different Holding Times on The Microstructure of Al-Mg₂Si In-situ Cast Composite

A. Malekana, M. Emamy,M. Emamy,J. Ghiasinejad,M.R.Ghorbani 한국소성가공학회 2010 기타자료 Vol.2010 No.6

An isothermal reheating approach was used to study the effect of isothermal holding time on the microstructure of Al-Mg₂Si in-situ cast composite. Process temperature was selected at 590℃ which is in the semi solid state with respect to the phase diagram of Al-Mg₂Si system. The morphology of primary Mg₂Si particles was identified as irregular shape. The microstructures of the composite at two different states of reheated and as-cast, were compared to reveal the degree of particle modification. The results showed that higher holding time have more significance influence on the nodularity and also decreasing the size of primary Mg₂Si particles. An optimum time was also obtained for isothermal reheating processwhich can be affected by different parameters discussed in this work.

Mechanical and high temperature wear properties of extruded Al composite reinforced with Al₁₃Fe₄ CMA nanoparticles

Nemati, N.,Emamy, M.,Penkov, O.V.,Kim, J.,Kim, D.E. Elsevier Ltd 2016 Materials & Design Vol.90 No.-

<P>The mechanical and tribological properties of extruded aluminum matrix composites reinforced with various weight percentages (1, 3, 5, 7, 10 wt.%) of Al13Fe4 complex metallic alloys (CMAs) were investigated. The nano-composites were produced using conventional powder metallurgy and a hot extrusion process. The tribological behavior of the composites was investigated under normal loads in the range of 20-80 N using a reciprocating high-temperature tribo-tester over a temperature range of 25-350 degrees C. At an optimized reinforcing agent concentration of 5 wt.%, the composite showed a significant enhancement in Young's modulus (similar to 108 MPa) and hardness (similar to 1.85 GPa). The lowest coefficient of friction of 0.1 was attained at a temperature of 250 degrees C with a reinforcing agent concentration of 5 wt.%. Also, the wear rate was reduced by a factor of similar to 25 compared to the unreinforced aluminum specimen. The significant improvement in the tribological properties of the nanocomposite was attributed to the enhanced mechanical properties due to severe plastic deformation incurred during the extrusion process and incorporation of well distributed CMA nanoparticles in the matrix which provided oobstacles for dislocation motion. Detailed microstructural analyses revealed that incorporation of the second phase to the Al matrix led to microstructure refinement and increased the hardness up to similar to 2 GPa. Furthermore, the nanoparticles aided in the formation of hard and temperature-resistant tribo-layers which reduced the wear rate of the composite (Al-5 wt.% Al13Fe4) down to 1.5 x 10(-4) at 250 degrees C. (C) 2015 Elsevier Ltd. All rights reserved.</P>

The Effect of Li Additions on Wear Properties of Al-Mg₂Si Cast In-situ Composites

M. R. Ghorbani,M. Emamy,J.Ghiasinejad,A. Malekan 한국소성가공학회 2010 기타자료 Vol.2010 No.6

Wear rate of a modified Al-Mg₂Si composite was studied by the use of a conventional pin-on-disc technique. In-situ Al-Mg₂Si composites (15, 20, 25 wt.%) were cast in a simple cylindrical mold. 0.3 wt.% Li was added into the molten composite to modify its microstructure. It has been found that Li addition decreases the mean size of primary Mg₂Si particles. The wear behavior of different composites at different rates revealed that Li addition increases the wear properties of Al-15%Mg₂Si to some extent but it did not have any significant influence on wear properties of two other composites.

Elucidating the Effects of Cu and Hot-Extrusion on Tensile Properties of Al–AlSb In Situ Composite

H. Rostami,M. Emamy,J. Rasizadeh Ghani,B. Pourbahari 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8

The microstructures, hardness and tensile properties of Al–AlSb-xCu in situ composites have been studied where the amountof Sb was 10 wt% and Cu contents were 1, 3, 5, 7 and 10 wt% Cu. Microstructural studies indicated that depending Cucontent, the crystals of primary AlSb alter seriously in shape and size, and also a new Cu-intermetallic (Al2Cu) is formedin the as-cast microstructure. Although T6 heat treatment did not afect primary AlSb phase, extrusion process refned itthrough fragmentation mechanism. A uniform microstructure including well distributed fne primary AlSb particles wasfound by adding 5 wt% Cu to the Al–AlSb composite, as an optimum content. The variation of hardness results with Cuaddition showed an increasing trend, while tensile testing examinations revealed that by exceeding Cu content (>5 wt%),the ultimate tensile strength (UTS) of the composites is reduced in both as-cast and T6 states. The efect of heat treatment onelongation improvement of the extruded composite was positive; however, it was reverse in as-cast condition, since extrudedspecimens showed a better response to removing the CuAl2 phase in the eutectic region during heat treatment. Remarkableenhancement in the UTS and elongation values of the extruded specimens, before and after heat treatment, was attributed tothe extensive fragmentation of intermetallic phases and well distributed fne particles in the matrix which provided properobstacles for dislocation motion. The fracture behavior of intermetallics in as-cast specimens showed more cleavage fracturein comparison with extruded and heat treated composites which demonstrated more dimples.

Effects of Al–5Ti–1B master alloy on the microstructural evaluation of a highly alloyed aluminum alloy produced by SIMA process

M. Alipour,M. Emamy,M. Azarbarmas,M. karamouz 한국소성가공학회 2010 기타자료 Vol.2010 No.6

This study was undertaken to investigate the influence of Al?5Ti?1B master alloy on the structural characteristics of Al?12Zn?3 Mg?2.5Cu aluminum alloy. The optimum amount of Ti containing master alloy for proper grain refining was selected as 6 wt.%. A modified strain-induced, melt-activated (SIMA) process for semi-solid processing of alloys was proposed. In order to examine the effectiveness of the modified SIMA process, the recrystallized microstructures of the Al alloy (Al?12Zn?3 Mg?2.5Cu) prepared by the modified SIMA processes were macroscopically. The modified SIMA process employed casting, warm multi-forging, recrystallization and partial melting instead of the conventional process. Reheating condition to obtain a fine globular microstructure was optimized. The microstructure evolution of reheated Al?12Zn?3 Mg?2.5Cu aluminum alloy was characterized by SEM (Scanning electron microscopy) and optical microscopy. In this study the relation between the induced strain with size and shape of grain size has been studied. Results indicated that with the increase of strain sphericity of particles, their size decreases and sphericity takes place in less reahiting time.

Effects of Boron on Microstructure and Tensile Properties of Al–Mg₂Si Metal Matrix Composite

M. Azarbarmas,M. Emamy,M. Alipour,M. karamouz 한국소성가공학회 2010 기타자료 Vol.2010 No.6

The effects of Boron (B) modification on the microstructure and tensile properties of an in situ prepared Al?15%Mg2Si composite were studied. The results show that the addition of B reduces the average size of primary Mg2Si particles from 25 to 15 μm and increases the amount of alpha phase. Meanwhile, with the addition of 3.0 wt.% B, The ultimate tensile strength (UTS) and elongation to rupture (Er) of the composite reach as high as 160 MPa and 4.7%, respectively. SEM images of the specimens showed that with the addition of B the pseudo-eutectic Al-Mg2Si refined ,that improved the ductility of specimens.

Synergistic Effects of Cerium-Based Rare Earth Addition and Hot Deformation on the Microstructure and Mechanical Properties of Mg-0.5Zn-0.5Zr Magnesium Alloy

Hooman Abedi,Massoud Emamy,Jafar Rassizadehghani,Hamed Mirzadeh 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.5

The effects of cerium-based rare earth (RE) addition and hot deformation via extrusion on the microstructure and mechanicalproperties of Mg-0.5Zn-0.5Zr alloy were studied. It was found that RE addition could effectively refine the as-cast microstructureup to 2 wt% RE with a notable grain refining effect up to 1 wt% RE. High RE additions resulted in a less effectivegrain refinement and the appearance of coarse dendritic microstructure. While the as-cast strength and ductility wereenhanced by increasing RE content up to 1 wt% due to grain refinement, alloys with high RE content faced a remarkable dropin total elongation and also showed lower ultimate tensile strength (UTS) values, which was related to the interconnectedintergranular brittle intermetallics (Mg12RE) with high volume fractions. For the extruded alloy with 1 wt% RE, besidesthe fragmentation and dispersion of intermetallics, a remarkable grain refinement due to the recrystallization processes wasobserved. Accordingly, the UTS of 415 MPa, total elongation of 17% and tensile toughness of 65.9 MJ/m3 were obtained afterextrusion, which are quite superior to the corresponding values of 210 MPa, 12% and 22.1 MJ/m3 for the as-cast counterpart,respectively. Regardless of the processing condition, the grain size effect was found to be the dominant factor in determiningthe yield stress (Hall–Petch law), where the deviation of this trend due to the presence of hard Mg12REphase was discussed.

Wear Behavior of Al-Mg2Si Cast In-situ Composite

J. Ghiasinejad,M. Emamy,M. R. Ghorbani,A. Malekan 한국소성가공학회 2010 기타자료 Vol.2010 No.6

Al-Mg₂Si in situ composites are great candidates for automobile brake discs due to their low density, reasonably high young"s modulus and low thermal expansion coefficient. Thus, understanding wear properties of this composite is of a great importance. In this study wear behavior of an in-situ Al-Mg₂Si composite, prepared from a simple casting route, has been investigated using a pin-on-disc configuration concerning the effect of Mg₂Si volume fractions, 15, 20 and 25% respectively. It was found that the weight loss increases with increase in reinforce volume fraction which can be due to a coarse morphology of primary Mg₂Si particles. It was found that the variations of weight loss with sliding distance comprise different regimes of which the mechanisms are discussed.

Influence of Hot Extrusion on the Microstructure, Tensile and Wear Properties of Mg–5Sb–xSiC Hybrid Composites

M. Ra’ayatpour,M. Emamy,J. Rassizadehghani 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.3

The structure, hardness, tensile and wear behavior of Mg–5Sb–xSiC hybrid composites experimented where the amountof SiC particles were 1, 3, and 5 wt% SiCp before and after applying hot extrusion process. Micron size SiC particles wereadded to Mg–5Sb alloy via stir casting technique to form both Mg3Sb2and SiC particles in the as-cast microstructures. Although SiC addition reduced the grain size of the Mg–5%Sb in-situ metal matrix composite (MMC), no improvement wasobserved on ultimate tensile strength (UTS) and the ductility (EL.%) in the as-cast state. The use of the extrusion processled to a remarkable fracturing of Mg3Sb2intermetallic along the extrusion direction, grain refinement, and reduction in thesize of SiC clusters. The optimal amount of SiC was found to be 3 wt%, which reduced the grain size from ~ 827 to ~ 4 μmand promoted the UTS amounts from 120 to 244 MPa for as-cast and hot extruded composites. Besides, the enhancementof yield strength of extruded MMCs was rationalized depending on the grain size compared to the as-cast condition. Thefractography of the as-cast composites revealed more cleavage planes in contrast with hot extruded composites, which provedmuch more dimples. It was also found that the use of hard SiC particles in hybrid composite improved wear properties justin the extruded state. According to observations, in various sliding test conditions, the abrasive, oxidation and delaminationare mostly operated in combination.

The Microstructure and Tensile Properties of a Newly Developed Mg–Al/Mg3Sb2 In Situ Composite in As-Cast and Extruded Conditions

A. Montajabnia,B. Pourbahari,M. Emamy 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.5

The microstructures and tensile properties of Mg–x wt%Al–y wt%Sb alloys have been studied where x/y ratio was 1 andSb(Al) contents were 5, 10, 15 and 20 wt%, respectively. The results indicated that by increasing Sb(Al) content, not onlythe crystals of primary Mg 3 Sb 2 alter from small fl ake-like particles to polygonal or needle-like morphology, but also theeutectic structure changes from semi-continuous network in Mg–5Al–5Sb to continuous network in Mg–20Sb–20Al alloy. The results obtained from thermal analysis revealed different peaks related to the formation of Mg 3 Sb 2 as primary phase andeutectic structure containing Mg 17 Al 12 + Al 3 Mg 2 intermetallic phases. Further results also revealed that Sb(Al) additionschange the solidification performance of the material by depressing the Mg 3 Sb 2 nucleation temperature, reducing solidifi -cation range and widening eutectic area. Tensile testing results showed that with the increase in Sb (Al) content, ultimatetensile strength (UTS) and elongation values of the alloys are decreased in as-cast condition. But, signifi cant improvement inthe UTS and elongation values of the extruded specimens was attributed to the severe fragmentation of intermetallic phasesand well distributed fi ne particles in the matrix which provided proper obstacles for dislocation motion. It was interesting tonote that the fracture behavior of intermetallic particles was found to be different, while Mg 3 Sb 2 was ductile, intermetalliccompounds in eutectic regions were brittle.