Grain refinement of an Al-2 wt%Cu Alloy by Al3Ti1B master alloy and ultrasonic treatment

Both inoculation by AlTiB master alloys and Ultrasonic Treatment (UT) are effective methods of refining the grain size of aluminium alloys. The present study investigates the influence of UT on the grain refinement of an Al-2 wt% Cu alloy with a range of Al3Ti1B master alloy additions. When the alloy contains the smallest amount of added master alloy, UT caused significant additional grain refinement compared with that provided by the master alloy only. However, the influence of UT on grain size reduces with increasing addition of the master alloy. Plotting the grain size data versus the inverse of the growth restriction factor (Q) reveals that the application of UT causes both an increase in the number of potentially active nuclei and a decrease in the size of the nucleation free zone due to a reduction in the temperature gradient throughout the melt. Both these factors promote the formation of a fine equiaxed grain structure

The role of ultrasonically induced acoustic streaming in developing fine equiaxed grains during the solidification of an Al-2% Cu alloy

Recent research and a simulation of heat transfer and solidification during acoustically generated convection showed that the location of the coolest liquid, and thus the place where the first grains are expected to form, is under the sonotrode. Further, the generated vigorous convection produces a very flat temperature gradient in the bulk of the melt facilitating the formation of a refined equiaxed structure throughout the casting. This study validates these findings through a series of experiments on an Al-2 wt pct Cu alloy, which evaluate grain formation under the sonotrode over time and relate this to the formation of the macrostructure of a cast ingot. Analysis of the results confirms the predictions of the simulation and shows that, for the conditions applied, most grains nucleated in the cavitation zone are swept into the melt by acoustically generated convection and, over a period of 70 seconds, the number of grains increase and they grow with spherical and globular morphology gradually filling the casting with refined equiaxed grains. It was found that the macrostructure of each casting is made up of three microstructural zones. A fine grained equiaxed zone forms from the bottom of the casting due to settling of grains during and after termination of ultrasonic treatment (UST), which increases in size with the increasing duration of UST. Above this zone, a coarse-grained structure is formed due to depletion of UST-generated grains on termination of UST. At the top of the casting, a zone of columnar grains growing from the top surface of the melt is formed. The latter two zones decrease in size with the increasing UST duration until 80 seconds, when the macrostructure consists entirely of the equiaxed zone. (C) The Minerals, Metals & Materials Society and ASM International 201

The role of ultrasonic treatment in refining the as-cast grain structure during the solidification of an Al–2Cu alloy

The effect of Ultrasonic Treatment (UT) over selected temperature ranges during cooling and solidification of an Al–2Cu alloy melt on the grain structure and cooling behaviour of the alloy has been investigated using a molybdenum sonotrode introduced without preheating. UT was applied over various temperature ranges before, during and after the nucleation of primary aluminium grains.It was found that ultrasonic grain refinement was achieved only when UT was applied from more than 20 °C above the liquidus temperature until below the liquidus temperature after nucleation has occurred. Applying UT from 40 °C or 60 °C above the liquidus to just above the liquidus brings the melt to a condition that favours nucleation,survival of the nucleated grains and their subsequent transport throughout the melt. Continuing to apply UT beyond the liquidus for a short time enhances both nucleation and convection thereby ensuring the formation of a fine, uniform equiaxed grain size throughout the casting.The lack of grain refinement when UT was applied from 20 °C above the liquidus temperature or from temperatures below the liquidus temperature is attributed to the formation of a strong solidified layer on the sonotrode which hinders the effective transmission of ultrasonic irradiation into the liquid metal. The application of a preheated sonotrode showed that formation of a solid layer can be prevented by preheating the sonotrode to 285 °C. Thus,an appropriate amount of superheat of the liquid metal or sufficient reheating of the sonotrode is necessary for ultrasonic grain refinement when a sonotrode is introduced into the melt.ARC Centre of Excellence for Design in Light Metals, ARC Discovery Project DP140100702, and the ExoMet Project co-funded by the European Commission׳s 7th Framework Programme (contract FP7-NMP3-LA-2012-280421), by the European Space Agency and by the individual partner organisations

Microstructure and mechanical properties of high pressure die cast magnesium alloy AE42 with 1% strontium

The addition of 1 wt-%Sr to AE42 results in an improvement in the tensile strength of the alloy at elevated temperatures of 150 and 175degreesC and an improvement in the constant load creep properties at 175degreesC. The improved elevated temperature tensile and creep strength of the alloy can be attributed to the presence of a strontium-containing phase in the microstructure of the alloy along with an increase in the stability of the microstructure of the alloy at high temperatures. (C) 2004 W. S. Maney Son Ltd

Finite element analysis of porous commercially pure titanium for biomedical implant application

In biomedical implant applications, porous metallic structures are particularly appealing as they enhance the stiffness compatibility with the host tissue. The mechanical properties of the porous material are critically affected by microstructural features, such as the pore shape, the distribution of porosity, and the level of porosity. In this study, mechanical properties of porous commercially pure titanium structures with various porosity levels were investigated through a combination of experiments and finite element modelling. Finite element simulations were conducted on representative volume elements of the microstructure to assess the role of pore parameters on the effective mechanical properties. Modelling results indicated that the shape of the pore, in addition to porosity level, play a significant role on the effective behaviour. Finite element simulations provide reasonably accurate prediction of the effective Young’s modulus, with errors as low as 0.9% for porosity of 35%. It was observed that the large spread in yield strength produced by the simulations was most likely due to the random pore distribution in the network, which may lead to a high probability of plastic strain initiation within the thin walls of the porous network

Role of ultrasonic treatment, inoculation and solute in the grain refinement of commercial purity aluminium

The present study investigates the influence of ultrasonic treatment on the grain refinement of commercial purity aluminium with a range of Al3Ti1B master alloy additions. When the aluminium contains the smallest amount of added master alloy, ultrasonics caused significant additional grain refinement compared to that provided by the master alloy alone. However, the influence of ultrasonics on grain size reduces with increasing addition of the master alloy which adds additional TiB2 particles and Ti solute with each incremental addition. Applying the Interdependence model to analyse the experimentally measured grain sizes revealed that the results of this study and those from similar experiments on an Al-2Cu alloy were consistent when the alloy compositions are converted to their growth restriction factors (Q) and that increasing Q had a major effect on reducing grain size and increasing grain number density. Compared with the application of ultrasonic treatment where an order of magnitude increase in the grain number density is achieved, an increase in the Ti content over the range of master alloy additions, causes the grain number density to increase by approximately three times