Study of Microstructural Evolution and Phase’s Morphology after Partial Remelting in A356 Alloy

2008 ◽  
Vol 141-143 ◽  
pp. 367-372 ◽  
Author(s):  
A. Mahdavi ◽  
M. Bigdeli ◽  
M. Hajian Heidary ◽  
F. Khomamizadeh
Keyword(s):  
Dendritic Structure ◽  
A356 Alloy ◽  
Intermetallic Phases ◽  
Effective Parameters ◽  
Dendritic Microstructure ◽  
Globular Structure ◽  
Needle Morphology ◽  
Sima Process ◽  
Semi Solid ◽  
Globular Form

In this work, effective parameters of SIMA process to obtain non dendritic microstructure in A356 alloy were investigated. In addition, the effect of SIMA process on the evolution of morphology of silicon and intermetallic phases in this alloy was studied. Microstructure images obtained from optical microscopy and SEM observation showed that increase in plastic work up to 40% and then holding of samples in the semi solid state at temperature of 580oC, causes that primary dendritic structure changes to non dendritic, fine and globular structure, but optimum reheating time completely depended on initial thickness of samples. If all parameters of SIMA process are the same, the grain boundaries of thinner samples begin to wet and following globalization will be completed in shorter reheating time rather than thicker ones. Moreover, it was found that the intermetallic phases lost their angular or needle morphology and gradually changed to rounded morphology and even to globular form. Also the optimum reheating time thoroughly depends on primary casting microstructure as the finer casting microstructure begin to globalize faster than thicker one under more little stains.

Microstructure Evolution of Conventional and Semi-Solid A356 Alloy with Addition of Strontium

2015 ◽  
Vol 1087 ◽  
pp. 488-492
Author(s):  
Yuan Sieng Seo ◽  
Laila Masrur Mohd Nasir ◽  
Hussain Zuhailawati ◽  
Anasyida Abu Seman
Keyword(s):  
Phase Analysis ◽  
Eutectic Alloy ◽  
Cast Alloy ◽  
Dendritic Structure ◽  
A356 Alloy ◽  
Melting Furnace ◽  
Eutectic Structure ◽  
Globular Structure ◽  
Semi Solid ◽  
Steel Mould

In this study, modification of aluminium silicon eutectic alloy by grain modifier, strontium was investigated on conventional and slope cast A356 alloy. A356 alloy with addition of 0 to 0.97 wt.% Sr was prepared by conventional and slope casting in melting furnace. The molten metal of A356 alloy was casted into steel mould. Microstructure was observed using SEM. Phase analysis was done using XRD. Microhardness was conducted using Vicker microhardness. Microstructure of conventional cast displayed dendritic structure whereas slope cast displayed globular structure. Addition of Sr refined eutectic structure in both conventional and slope cast alloy. Phase analysis revealed the presence of Al2Sr phase in conventional cast Al-6Si-0.97Sr. Microhardness of the conventional cast alloy decreased with increasing of Sr up to 0.97 wt.%.

Microstructure Evolution of Conventional and Semi-Solid Cast of A356 Aluminium Alloy with Addition of Inoculant

2015 ◽  
Vol 819 ◽  
pp. 25-30 ◽  
Author(s):  
M.N. Laila Masrur ◽  
M. Syukron ◽  
H. Zuhailawati ◽  
A.S. Anasyida
Keyword(s):  
Aluminium Alloy ◽  
Dendritic Structure ◽  
A356 Alloy ◽  
Optical Microscope ◽  
Globular Structure ◽  
Average Grain Size ◽  
Semi Solid ◽  
Vicker’S Microhardness ◽  
Steel Mould ◽  
A356 Aluminium Alloy

This paper investigated the effect of inoculant, Al-5Ti-1B in conventional and semi-solid casting A356 aluminium alloy. A356 aluminium alloy was melted at 850 oC and poured at 680 °C directly into the steel mould and on the inclined slope into steel mould. Inoculant was added in various percentages of 1 wt.%, 2 wt.%, 3 wt.% and 3.5 wt.% in A356 aluminium alloy melt. Microstructure and microhardness were characterized using optical microscope and Vicker’s microhardness tester. The addition of master alloy up 3.5 wt.% Al-5Ti-1B in conventional casting refined dendritic structure with average grain size of 33.41 μm. The microstructures of semi-solid A356 aluminium alloy with addition of Al-5Ti-1B consist of equiaxed structure of α-Al. Further addition of Al-5Ti-1B refined the globular structure of α-Al. The higher hardness was achieved for A356 alloy prepared using semi-solid with addition of 3.5 wt.% of Al-5Ti-1B.

Investigation of Fusion Weldments of Semi-Solid Aluminium A356 Alloy: Pool Geometry and Microstructure

2013 ◽  
Vol 765 ◽  
pp. 751-755 ◽  
Author(s):  
S. Sandhya ◽  
G. Phanikumar
Keyword(s):  
Fusion Zone ◽  
A356 Alloy ◽  
Welding Process ◽  
Fusion Welding ◽  
Thermal Gradients ◽  
Dendritic Microstructure ◽  
Evolution Simulation ◽  
Globular Microstructure ◽  
Gas Tungsten Arc ◽  
Semi Solid

A fusion welding technique to join a semi-solid processed A356 cast plate is explored using Gas Tungsten Arc Welding (GTAW). Semi-solid metal (SSM) billets of non-dendritic microstructure produced by rheocasting in a mould placed inside a linear electromagnetic stirrer were used for this study. GTAW experiments were conducted to simulate different thermal gradients near the fusion zone. The geometries of the weld pool as well as the temperature gradient in the fusion boundary were measured to understand the microstructure evolution. Simulation of the welding process was performed to aid in the analysis. Quantitative metallography provided the shape factor as a measure of globularity of the primary a-Al phase. Based on the studies, a model has been proposed to explain the observation of globular microstructure in the fusion zone of the welds. Conclusions show a positive correlation of thermal gradient with globular microstructure formation in this class of alloys.

Effect of Direct Current on the Semi-Solid Isothermal Heat-Treated Microstructure of ZA84 Magnesium Alloy

2011 ◽  
Vol 189-193 ◽  
pp. 871-875
Author(s):  
Ming Bo Yang ◽  
Xiao Feng Liang ◽  
Yi Zhu
Keyword(s):  
Direct Current ◽  
Current Density ◽  
Dendritic Structure ◽  
Isothermal Treatment ◽  
Structure Evolution ◽  
Dendritic Microstructure ◽  
Experimental Conditions ◽  
Isothermal Temperature ◽  
Heat Treated ◽  
Semi Solid

The effect of direct current on the semi-solid isothermal heat-treated microstructure of ZA84 alloy is investigated. The results indicate that it is possible to produce ZA84 alloy with non-dendritic microstructure by semi-solid isothermal treatment. Furthermore, imposing direct current during the semi-solid isothermal treatment of ZA84 alloy can accelerate the non-dendritic structure evolution of the alloy. Under the experimental conditions of this work, higher the current density, quicker is the rate of non-dendritic structure evolution for the semi-solid isothermal heat-treated ZA84 alloy. Further investigations need to be considered in order to optimize the current density, isothermal temperature and holding time.

The Effect of Initial Microstructure of A356 Alloys on the Mechanical Behavior in the Semisolid State

2006 ◽  
Vol 116-117 ◽  
pp. 449-452 ◽  
Author(s):  
Zhi Liang Ning ◽  
H. Wang ◽  
Jian Fei Sun
Keyword(s):  
Strain Rate ◽  
Dendritic Structure ◽  
A356 Alloy ◽  
Rate Sensitivity ◽  
Process Conditions ◽  
Semisolid State ◽  
Globular Structure ◽  
Initial Microstructure ◽  
Wide Range ◽  
Semisolid Casting

The quality of semisolid casting largely depends on the formability of the semisolid feedstock. Despite of the semisolid casting process conditions, the initial microstructure of the feedstock plays a significant role in determining the metal formability under the semisolid state. In this study, the effect of initial microstructure of A356 alloy on the mechanical forming response in its semisolid state was investigated. A wide range of the initial microstructures varied from a very coarse dendritic structure to a fine globular structure were produced in A356 alloy using the Controlled Nucleation Method, particularly by controlling pouring temperature during solidification. Cylindrical specimens with 12 mm in diameter and 10 mm in height were compressed to a height reduction of 8 mm at constant strain rates from 1.3910-1 /s to 1.3910-3 /s. Strain rate jump tests were also carried out in order to evaluate the strain rate sensitivity at high fraction solid of 0.9. The materials produced with a low superheat exhibit a fine globular structure. They showed a very low compression stress in the semisolid state compared with the materials poured at high temperatures, which have coarse and dendritic structure.

Effect of Titanium on Microstructure of Al2014 Alloy Prepared by SIMA Process

2013 ◽  
Vol 553 ◽  
pp. 93-98 ◽  
Author(s):  
M. Amuei ◽  
M. Emamy ◽  
R. Khorshidi
Keyword(s):  
Grain Size ◽  
Cold Working ◽  
Titanium Content ◽  
Optimum Amount ◽  
Globular Structure ◽  
Globular Microstructure ◽  
Heat Treated ◽  
Sima Process ◽  
Cold Worked ◽  
Semi Solid

Forming in semi-solid state to achieve globular microstructure has an effective influence on mechanical properties of aluminum alloys. In this research, the Al2014 alloy was prepared by a semi-solid strain-induced melt activated (SIMA) process. In order to analyze the effect of titanium content on the macrostructure of Al2014, the optimum amount of titanium according to its efficiency on reducing the grain size was obtained. Then, specimens with optimum titanium content were prepared by the SIMA process. Cold working was applied on specimens by an upsetting technique. Cold worked specimens were heat treated at 595, 605, 615, 625 and 635°C and were kept at these temperatures for 30 min to achieve a globular structure. Observations through optical and scanning electron microscopy (SEM) revealed that by increasing the temperature, an increase in sphericity and grain size occurs. According to the results, optimum condition in order to achieve a fine and globular microstructure is keeping specimens at 625°C for 30 min.

Prepartion of Semisolid AM60 Alloy by Novel Self-Inoculation Method

2011 ◽  
Vol 189-193 ◽  
pp. 3804-3809 ◽  
Author(s):  
Yuan Dong Li ◽  
Bo Xing ◽  
Ying Ma ◽  
Ti Jun Chen ◽  
Yuan Hao
Keyword(s):  
Slope Angle ◽  
Dendritic Structure ◽  
Primary Phase ◽  
Chemical Pollution ◽  
Cooling Channel ◽  
Dendritic Microstructure ◽  
Pouring Temperature ◽  
Inoculation Method ◽  
Semi Solid ◽  
Slurry Preparation

A research focus on semi-solid metal processing is the preparation of semi-solid slurry with non-dendritic microstructure. During the past several decades, people tended to obtain the non-dendritic structure by stirring melt of alloy which downs to the semi-solid temperature range, such as mechanical stirring and electromagnetic stirring; In recent years, with the technological innovation of semi-solid slurry preparation turned to be more convenient and efficient, most of these processes are based on the control of nucleation and growth process of primary phase during solidification, such as NRC, SSR, SLC, SEED, and CRP. In this paper, a novel process, named as “Self-Inoculation Method (SIM)”, has been proposed for semi-solid slurry preparation. The process involves self-inoculants addition to the melt, and then pouring the melt to mould through a multi-stream mixed cooling channel. The melt was avoided chemical pollution due to the particles of self-inoculants from the same composition as the melt. The semi-solid billets of AM60 alloy with non-dendritic structure were prepared by SIM. The effects of process parameters on the microstructure and the mechanism on refinement of alloy were investigated. The results indicate that pouring temperature, addition amount of self-inoculants and slope angle of the cooling channel are key factors for SIM process. The optimized parameters for the billet preparation of AM60 alloy are obtained: pouring temperature is at 680°C~700°C；addition of self-inoculants are between 5%~7% (mass fraction)；slope angle of the cooling channel is at 30°~45°. The heterogeneous nucleation was enhanced as the addition of self-inoculants; the formation of chill crystal and the fragmentation of dendrites because of cooling and shearing of the cooling channel, resulting in the increase of grains density and a small grain size.

Characterization of Globular Microstructure in NMS Processed Aluminum A356 Alloy: The Role of Casting Size

2011 ◽  
Vol 264-265 ◽  
pp. 1868-1877 ◽  
Author(s):  
Farshad Akhlaghi ◽  
Amir H.S. Farhood
Keyword(s):  
A356 Alloy ◽  
Systematic Investigation ◽  
Globular Structure ◽  
Near Net Shape ◽  
Size And Morphology ◽  
Semi Solid ◽  
Aluminum A356 Alloy ◽  
Processing Steps

Semi-solid processing (SSP) technology, due to its ability to provide near-net-shape components with properties far exceeding those of other casting technologies is considered as an alternative for forgings and investment castings. Conventional semi-solid forming, involving the use of heated billets, melt stirring or using cooling slopes require many processing steps and supplementary equipments. This article describes Narrow Melt Stream (NMS), as an alternative process for semi-solid processing of aluminum alloys that eliminates capital cost expenditures, reduces the number of steps required, and hence reduces the costs of making components with a globular structure. However, the applicability of this technique in producing globular structures in the large molds has not been explored. In the present study the results of a systematic investigation on the effects of mold size on the size and morphology of the globular structures formed by NMS processing of Al 356 alloy is reported. For this purpose, five different series of molds were employed. Each series consisted of three molds with identical volumes but different casting moduluses. By using these molds, the effects of casting modulus at constant casting size as well as the effect of casting volume on the size and shape factor of the globular structures in aluminum A356 samples prepared by NMS technique is reported.

Formation Mechanism of Thixotropic Microstructure of AM60 Alloy during Solidification

2014 ◽  
Vol 1030-1032 ◽  
pp. 86-89
Author(s):  
Bo Xing
Keyword(s):  
Formation Mechanism ◽  
Solid Substrate ◽  
Research Field ◽  
Primary Phase ◽  
Solid Particles ◽  
Metallographic Analysis ◽  
Semisolid Slurry ◽  
Dendritic Microstructure ◽  
Quenching Method ◽  
Semi Solid

A research field on semi-solid metal processing is the preparation of semi-solid slurry with non-dendritic microstructure. Nowadays, with the technological innovation of semi-solid slurry preparation, people turn to produce the non-dendritic semisolid microstructure by locally cooling of the alloy melt during solidification. Therefore, it is necessary to investigate the formation mechanism of the non-dendritic microstructure formation because the primary phase undergoes a specially controlled nucleation and growth which distinctly different from the commom solidification. In this paper, the semisolid slurry of AM60 alloy was produced by Self-Inoculation Method (SIM), and the microstructure evolution of primary α-Mg was investigated by water quenching method and metallographic analysis. The results indicate that the semisolid microstructure of AM60 alloy produced by SIM composed of small and globular α-Mg particles, and these grains undergone a coarsing process during quiescent holding. The solid substrate caused by the fusion of solid particles and the dendritic fragments caused by melt flow caused the grain multiplication, and then the grain undergone a steadily growth because of the uniform temperature distribution, resulting in the increase of grains density and a small grain size of the AM60 semisolid slurry.

Continuous Casting of Magnesium Billets for Semi-Solid Processing

2005 ◽  
Vol 475-479 ◽  
pp. 517-520
Author(s):  
Hwa Chul Jung ◽  
Kwang Seon Shin
Keyword(s):  
Aluminum Alloys ◽  
Continuous Casting ◽  
Magnesium Alloys ◽  
Casting Process ◽  
Az91 Alloy ◽  
Attractive Alternative ◽  
Limited Information ◽  
Continuous Casting Process ◽  
Dendritic Microstructure ◽  
Semi Solid

Semi-solid processing is recognized as an attractive alternative method for the near net-shape production of engineering components. Although there has been a significant progress in semi-solid processing of aluminum alloys, very limited information is available on semi-solid processing of magnesium alloys, except for the thixomolding process. Continuous casting process has been utilized to produce the billets with the desirable cross-section at a reduced production cost for many metals, such as steel, copper and aluminum alloys. It has also been commercially utilized to produce the aluminum billets with non-dendritic microstructure for subsequent thixocasting process. However, continuous casting of magnesium billets for semi-solid processing has not yet been commercialized due to the difficulties involved in casting of magnesium alloys. In the present study, a continuous casting process has been developed for the production of the cylindrical billets of magnesium alloys for the subsequent thixocasting process. In order to obtain the desired non-dendritic microstructure with an excellent degree of homogeneity both in microstructure and composition, an electromagnetic stirring system has been utilized. A continuous casting process has been proven to be an efficient way to produce the high quality billets of magnesium alloys for semi-solid processing. A prototype air conditioner cover was produced using the continuously cast billets of AZ91 alloy.

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