Microstructure modeling of a sintered Al–4Si–0.6Mg alloy extruded at semi-solid temperature ranges

Author(s):  
Abeyram M Nithin ◽  
M Joseph Davidson ◽  
Chilakalapalli Surya Prakash Rao

The microstructure evolution of sintered and extruded samples of Al–4Si–0.6Mg powder alloys at various semi-solid temperature ranges of 560 °C, 580 °C, and 600 °C, holding times of 600, 1200, and 1800 s, and strain rates of 0.1, 0.2, and 0.3 s−1 was studied. From the stress–strain curves and metallographic studies, Arrhenius grain growth model and Avrami dynamic recrystallization model have been formulated by means of linear regression. Parameters such as peak strain, critical strain, recrystallization fraction, and material constants have been found using the above equations. The experimental and calculated values of various material parameters agree with each other, indicating the accuracy of the developed model. Finite element method-based simulations were performed using DEFORM 2D software, and the average grain size obtained from experiments and simulations was validated by means of average grain size. The relative density of the compacted specimens as well as the extruded specimens was also simulated. The simulation results showed that large grains appeared at high temperatures and at the bottom of the specimen.

2016 ◽  
Vol 256 ◽  
pp. 257-262 ◽  
Author(s):  
Yong Fei Wang ◽  
Sheng Dun Zhao ◽  
Chen Yang Zhang

Semi-solid AlMg0.7Si alloy was prepared by recrystallization and partial melting (RAP) method which including radial forging (RF) and remelting process. RF was carried out with different area reduction ratios (ARRs) to accumulate strains, effect of ARR and remelting time on microstructure was studied, mechanism of RAP preparing semi-solid AlMg0.7Si alloy was summarized. Results show that, compared with the large and irregular solid grains form remelting of starting material, solid grains of semi-solid alloy prepared by RAP are fine and globular, and the optimum microstructure can be obtained when alloy with 80% ARR is remelted at 630 °C for 10 min. With the increase of ARR, the solid grains are smaller and rounder. With the increase of remelting time, the average grain size is increased, and the spheroidization degree of solid grain is gradually improved. The main mechanism consists of pre-deformation, recovery and recrystallization, grains fragmentation, grains spheroidization and coarsening.


Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 153 ◽  
Author(s):  
Takashi Kuwahara ◽  
Taro Osaka ◽  
Mizuki Saito ◽  
Shinsuke Suzuki

A2024 alloy foams were fabricated by two methods. In the first method, the melt was thickened by Mg, which acts as an alloying element (melt route). In the second method, the melt was thickened by using primary crystals at a semi-solid temperature with a solid fraction of 20% (semi-solid route). A2024 alloy foams fabricated through the semi-solid route had coarse and uneven pores. This led to slightly brittle fracture of the foams, which resulted in larger energy absorption efficiency than that of the foams fabricated through the melt route. Moreover, A2024 alloy foams fabricated through the semi-solid route had a coarser grain size because of the coarse primary crystals. However, by preventing the decrease in the alloying element Mg, the θ/θ’ phase was suppressed. Additionally, by preventing the precipitation of the S′ phase, the amount of Guinier-Preston-Bagaryatsky (GPB) zone increased. This resulted in a larger plateau stress.


2006 ◽  
Vol 116-117 ◽  
pp. 132-135 ◽  
Author(s):  
Ju Fu Jiang ◽  
Shou Jing Luo

By using equal channel angular extrusion (ECAE) as strain induced step in strain induced melt activated (SIMA) and completing melt activated step by using semi-solid isothermal treatment, a new SIMA method is introduced firstly. The results show that semi-solid billet with highly spheroidal and homogeneous grains with the average grain size of 20μm can be prepared by new SIMA method. High mechanical properties, such as ultimate tensile strength of 321.8MPa and elongation of 15.2% are obtained in magazine plate components thixoforged using semi-solid billet prepared by new SIMA.


The microstructure and radiation resistance of T91 martensitic steel were studied after thermomechanical treatment. The physical and technological foundations of the process of creating of a nanostructured state in T91 reactor steel have been developed. This structure was received by severe plastic deformation of T91 steel by the multiple “upsetting-extrusion” method (developed at the NSC KIPT) in two temperature ranges of deformation: in the region of austenite existing and with a successive decrease in the deformation temperature and an increase in cycles of “upsetting-extrusion” in the field of ferrite existence. For the further heat treatment the particular temperature range and deformation modes were chosen to obtain optimal structure. Also, the optimum temperature of tempering to receive the uniform structure was established. It was found that the average grain size of T91 steel decreases from 20 μm in the initial state to ~ 140 nm after 5 cycles of “upsetting-extrusion” in the ferrite interval and to ~ 100 nm after 3 cycles of deformation in the austenitic region. It was determined that with an increase in the number of cycles and a decrease in the deformation temperature, a rise in the degree of uniformity of grain size distribution occurs. In this case, the microhardness increases from 2090 MPa to 2850 MPa after 5 cycles of “upsetting-extrusion” in the ferritic interval. In the austenitic region, the microhardness values increase from 3400 to 3876 MPa. The swelling of T91 steel in two structural states, martensitic and ferritic, was determined. Thus, steel swelling at a high dose of irradiation with argon ions with an energy of 1.4 MeV (120 displacements per atom, irradiation temperature 460 ° C) is ΔV / V = 0.26% in the initial state (martensitic structure) and 0.65% for samples with a ferritic structure.


2012 ◽  
Vol 192-193 ◽  
pp. 130-135
Author(s):  
Shu Sen Wu ◽  
Chong Lin ◽  
Shu Lin Lü ◽  
Ping An

The microstructure and mechanical properties of Al-17Si-2Fe-2Cu-1Ni (mass fraction, %) alloys with 0.4% or 0.8% Mn produced by semi-solid casting process were studied. The semi-solid slurry of the alloys was prepared by ultrasonic vibration (USV) process. With USV process, the average grain size of primary Si in the alloys could be refined to 21~24μm, whether with or without P modification. The P addition has no further refinement effect on the primary Si in the case of the combined use of USV with P addition. Without USV, the alloys contain a large amount of long needle-like β-Al5(Fe,Mn)Si phase and plate-like δ-Al4(Fe,Mn)Si2 phase. Besides, the alloy with 0.8% Mn contains a small amount of coarse dendritic α-Al15(Fe,Mn)3Si2 phase. With USV treatment and semi-solid casting process, the Fe-containing compounds in the alloys are refined and exist mainly as δ-Al4(Fe,Mn)Si2 particles with average grain size of about 18μm, and only a small amount of β-Al5(Fe,Mn)Si phase is remained. With USV treatment and without P modification, the ultimate tensile strengths (UTS) of the alloys containing 0.4% and 0.8%Mn produced by semi-solid process are 260MPa and 270MPa respectively at room temperature, and the UTS are 127MPa and 132MPa at 350°C.


2013 ◽  
Vol 58 (1) ◽  
pp. 95-98 ◽  
Author(s):  
M. Zielinska ◽  
J. Sieniawski

Superalloy René 77 is very wide used for turbine blades, turbine disks of aircraft engines which work up to 1050°C. These elements are generally produced by the investment casting method. Turbine blades produced by conventional precision casting methods have coarse and inhomogeneous grain structure. Such a material often does not fulfil basic requirements, which concern mechanical properties for the stuff used in aeronautical engineering. The incorporation of controlled grain size improved mechanical properties. This control of grain size in the casting operation was accomplished by the control of processing parameters such as casting temperature, mould preheating temperature, and the use of grain nucleates in the face of the mould. For nickel and cobalt based superalloys, it was found that cobalt aluminate (CoAl2O4) has the best nucleating effect. The objective of this work was to determine the influence of the inoculant’s content (cobalt aluminate) in the surface layer of the ceramic mould on the microstructure and mechanical properties at high temperature of nickel based superalloy René 77. For this purpose, the ceramic moulds were made with different concentration of cobalt aluminate in the primary slurry was from 0 to 10% mass. in zirconium flour. Stepped and cylindrical samples were casted for microstructure and mechanical examinations. The average grain size of the matrix ( phase), was determined on the stepped samples. The influence of surface modification on the grain size of up to section thickness was considered. The microstructure investigations with the use of light microscopy and scanning electron microscopy (SEM) enable to examine the influence of the surface modification on the morphology of ’ phase and carbides precipitations. Verification of the influence of CoAl2O4 on the mechanical properties of castings were investigated on the basis of results obtained form creep tests.


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