Grain Size Of Castings Research Articles

Considerations on the effect of solutal on the grain size of castings from superheated melts

The amount of solutal present in an alloy affects the grain size of the cast metal as solute is rejected at the solidification front. This is normally quantified using the so called growth restriction factor Q. This work presents some considerations about the effect of solutal on the final cast structure with a focus on the nature of the alloy system, the effect of non-equilibrium solidification conditions and the effect of superheating of the molten metal.

Effect of a Minor Sr Modifier on the Microstructures and Mechanical Properties of 7075 T6 Al Alloys

The influence of a minor strontium (Sr) modifier on the microstructures and mechanical properties of 7075 Al alloys was investigated in this paper. The grain size of cast 7075 Al alloys was refined from 157 μm to 115 μm, 108 μm, and 105 μm after adding 0.05 wt. %, 0.1 wt. %, and 0.2 wt. % Sr, respectively. The extruded 7075 Al alloys was refined with different degrees of Sr modifier. The mechanical properties were optimum when adding 0.1 wt. % Sr. The ultimate tensile strength (σb) increased from 573 to 598 MPa and the elongation-to-failure (δf) was raised from 19.5% to 24.9%. The microhardness increased from 182 to 195 Hv. The tensile fracture surface via scanning electron microscopy (SEM) revealed a transition from brittle fracture to ductile fracture as Sr increased from 0 wt. % to 0.2 wt. %. The result in this paper proved that the modifier can improve the properties of 7075 Al alloy.

Preiskava vpliva časa zadrževanja in mešanja taline na zmanjšanje velikosti zrn zlitine A206

Effects of melt stirring and holding time were studied with an Al-4.5 % of mass fractions of Cu (A206) alloy. The optimum level of a grain refiner was determined in conjunction with both continuously stirred and non-stirred melts during the holding time. Results showed that a mass fraction of a Ti addition of as low as 0.03 % was sufficient to obtain the 82 μm average grain size, while a Ti addition exceeding the mass fraction of 0.03 % showed no significant effect on the grain size of castings. The grain refinement tends to fade with a long holding time in a non-stirred liquid. The results also showed that an effective grain refinement of the A206 alloy can be achieved with a long holding time as long as the liquid alloy is continually stirred.

Effect of Casting Modulus on Microstructure and Segregation in K441 Superalloy Casting

Four castings with different modulus have been designed to simulate different thickness sections of a turbine blade during casting process. The microstructure has been observed by optical microscopy (OM) and scanning electron microscopy (SEM). The micro-segregation was tested by energy dispersive spectroscopy (EDS) and the macro-segregation was analyzed by using Metalscan 2500 spectrometers. The experimental results show that the microstructure of casting is affected by modulus apparently. The smaller the modulus, the finer the microstructure. The average grain size of castings with modulus of 0.29, 1.57, 3.16 and 5.0 mm is 0.3, 1.5, 2.7 and 4.3 mm, and the volume fraction of eutectic is 0, 0.1%, 0.2% and 1.0%, respectively. The micro/macro segregation is affected by the modulus apparently. The smaller the modulus, the lower the segregation level. When the modulus of casting increases, the content of Al increases, while the content of W, Cr and Mo decreases both in inner grain and near grain boundary. The content of Al and Mo in inner grain is higher than that near grain boundary, while the content of Cr and W in inner grain is lower than that near grain boundary.

Processing and Alloy Development to Optimise the Properties and Cost-Effectiveness of Components Manufactured from TiAl-Based Alloys

The IRC has carried out a major research programme over the last ten or so years aimed at developing the processing and optimisation of TiAl-based alloys. This work has covered melting, the production of shaped castings, powder processing and a range of thermomechanical processing routes in parallel with alloy development. In this paper the work aimed at understanding the factors that influence the properties of thermo-mechanically processed and cast samples of TiAl-based alloys will be reviewed. It is shown that the use of boron to control the grain size of castings leads to limited ductility in the stronger and more highly alloyed TiAl alloys because ribbon-like borides up to 200µm in length can be formed. It is also shown that although a fully lamellar microstructure offers a good balance of properties their plastic anisotropy leads to pre-yield fracture and to reduced fatigue life. It is clear that grain size control is essential if an acceptable balance of properties is to be obtained but that if casting is to be used grain refinement via boron addition is not totally satisfactory. A simple heat treatment can be used to refine the microstructure of cast boron-free alloys, which leads to ductility comparable with that in wrought samples and the associated convoluted microstructure should also eliminate pre-yield cracking.

Melting and casting of FeAl-based cast alloy

The FeAl-based intermetallic alloys are of great interest because of their low density, low raw material cost, and excellent resistance to high-temperature oxidation, sulfidation, carburization, and molten salts. The applications based on these unique properties of FeAl require methods to melt and cast these alloys into complex-shaped castings and centrifugal cast tubes. This paper addresses the melting-related issues and the effect of chemistry on the microstructure and hardness of castings. It is concluded that the use of the Exo-Melt™ process for melting and the proper selection of the aluminum melt stock can result in porosity-free castings. The FeAl alloys can be melted and cast from the virgin and revert stock. A large variation in carbon content of the alloys is possible before the precipitation of graphite flakes occurs. Titanium is a very potent addition to refine the grain size of castings. A range of complex sand castings and two different sizes of centrifugal cast tubes of the alloy have already been cast.

Alの鋳造に関する研究(VI)Al合金の結晶微細化について

The grain refinement of aluminium alloy containing Cu 2.92% and Si 1.17% was mainly investigated by addition of NaF·BF3 or KF·TiF4 combined with salts. Results obtained are as follows: (1) The addition of a small amount of KF·TiF4 up to 0.02% gives scarecely any remarkable effect upon the grain refinement of castings. It is necessary to use a quantity of salts greater 0.02% of in order to obtain of NaF·BF3 finer grain size. (2) By the addition of more than 0.6%, the grain size of castings becomes very fine, especially when it is added together with a small amount of KF·TiF4 (0.007∼0.02%), the purpose can be achieved completely. Thus it is thought that effect was given by the simultaneous addition of B and Ti, moreover this effect was observed in the changing of the specific gravity of castings.

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