Papers by Author: Roger Grimes

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Authors: G.J. Mahon, D. Warrington, R. Butler, Roger Grimes
Authors: Roger Grimes, R.J. Dashwood, A. Dorban, M. Jackson, S. Katsas, I. Pong, G. Todd
Abstract: The early view of superplasticity was that it was a phenomenon that could only be exhibited by fine grained, two phase alloys. This effectively ruled out most alloys that possessed attractive service properties. The first material to demonstrate good superplastic properties from a virtually single phase microstructure was the Al-6%Cu-0.5%Zr, AA 2004 but this was followed by superplastic versions of AA7475, AA8090 and AA5083. Superplasticity was also demonstrated in magnesium based alloys at an early stage. More recently different grain control additions, such as scandium or erbium have been investigated and it has also been demonstrated that, in certain circumstances, aluminium simply with the addition of a grain controlling element can exhibit good superplastic behaviour. While conventional wisdom teaches that large fabricating strains are required to confer good superplastic properties in the sheet product, recent results with both aluminium and magnesium alloys cast doubt on this belief. Although, for many years, strip casting has appeared to provide an attractive semi-fabricating route for superplastic sheet problems with centre line segregation in alloys with a wide freezing range have precluded its use. It has been demonstrated that recent developments in strip casting enable production of alloys with as wide a freezing range as AA5182 to be cast with a fine, equiaxed grain structure across the strip thickness. The paper will review the state of these various developments and their implications for the manufacture of superplastic sheet materials.
Authors: A.J. Barnes, M.J. Stowell, Roger Grimes, D.B. Laycock, B.M. Watts
Abstract: Prior to 1969 the pioneering work carried out by Backofen and Fields in the USA and Johnson and Hundy in the UK demonstrated the 'promise' of Superplastic Forming. Using fine grained dual phase alloys, typically of eutectic or eutectoid compositions, they produced some of the very first superplastically formed prototype components. Although not always 'practical', these dual phase alloys were stable when heated and if appropriately processed often proved to be very superplastic. At that time 'dilute' alloys, including the majority of commercial aluminum alloys, having only a small volume fraction of alloying additions, were thought not to be capable of superplastic behavior due to their propensity to grain coarsen when heated. Breakthrough came in 1969 when at the research labs of Tube Investments, Hinxton Hall Nr Cambridge UK; the first 'SUPRAL' type dilute superplastic aluminum alloys were created. This paper describes the events and 'science' that led up to this development and the remarkable technology that has emerged since the authors began their superplasticity careers more than forty years ago. The future direction that this intriguing technology is likely to take is also explored.
Authors: Roger Grimes, R.J. Dashwood, H.M. Flower
Authors: Roger Grimes, R.J. Dashwood, H.M. Flower, M. Jackson, S. Katsas, G. Todd
Authors: R.J. Dashwood, Roger Grimes, A.W. Harrison, H.M. Flower
Authors: Richard J. Dashwood, David Klaumunzer, Martin Jackson, Zhong Yun Fan, Roger Grimes
Abstract: While magnesium alloys are routinely used in engineering applications in the form of net shape castings, applications for sheet product have been limited due to the poor cold formability of magnesium combined with the perceived expense of sheet. The issues associated with poor cold formability could largely be overcome if magnesium alloys were to be superplastically formed. Superplasticity in magnesium is well established with research papers on the subject dating back to the late 1960s. In recent years, interest in this area has grown to the point where a number of companies have successfully superplastically formed prototype automotive panels from magnesium alloy sheet. Concurrent to this the scientific community have demonstrated superplasticity in a wide range of magnesium alloys using processing techniques ranging from the exotic (severe plastic deformation) to the mundane (traditional warm rolling). Work by the current authors has shown, rather surprisingly, that superplasticity can be achieved in magnesium alloys in the as-cast condition. This has led to some initial exploratory work involving twin roll casting. The concept being that affordable superplastic magnesium sheet could be produced via twin roll casting with only limited rolling reduction to final gauge. This paper describes the superplastic behaviour (in uniaxial tension) and microstructure of sheet processed from strip cast AZ31 and AZ91. The experimental material has included strip cast AZ91 subjected to large shear strains immediately prior to casting. The material was tested in the as-cast condition and after warm rolling to a number of gauges. Industrially useful superplastic capability was demonstrated in the strip cast alloys. Furthermore, good superplastic capability was also demonstrated in sheet subsequently rolled from the cast metal and rolling strain did not significantly influence the ductilities obtained. The mechanism for achieving superplasticity in as-cast magnesium alloys will be considered and the contrasting deformation characteristics of AZ31 and AZ91 will be discussed in terms of m value analysis and microstructural characterisation.
Authors: H.M. Flower, G.J. Boyle, R.J. Dashwood, Roger Grimes
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