Materials Science Forum Vol. 735

Abstract: Fine grains were developed in Mg-3Al-1Zn (AZ31) alloy by isothermal caliber rolling at five different temperatures in the range of 250-450°C. The samples of different grain sizes were deformed by constant strain rate and differential strain rate test techniques over the temperature range of 220-450 °C and strain rate range of 10-5 to 10-1 s-1. The effects of grain size, test temperature and strain rate on flow st^{SuperscSuperscript text}ript textress were analysed to develop the constitutive relationship for sup^{Superscript text}erplastic deformation. The parameters of the constitutive relationship obtained from the constant strain rate tests and differential strain rate tests were used to find out the material constant A of the constitutive relationship.

Abstract: Aeronautic industry requires a high degree of precision on final thickness of superplastically formed sheets. However, for the same qualified process, an important dispersal of results was observed on final thickness of superplastically formed aluminium 7475-T4 industrial sheets, depending on the delivered sheet batch. After several cases of sheet batches that led to unachieved acceptance limit or cracking of the sheets during the process, ACB investigated aluminium 7475-T4 sheets quality at microscopic scale. Important grain size dispersal was observed and a heat treatment was successfully applied on sheets to diminish the grain size and improve the superplasticity of the sheets.

Abstract: Titanium is difficult to fabricate into complex aircraft configurations. There is several elevated temperature forming techniques that are available to produce titanium components for aircraft, two of which will be discussed here: Superplastic Forming (SPF) and hot forming. SPF is used when complex shapes are required, for example, tight radii, and uses a tool that contains the required configuration and seals around the periphery so inert gas pressure can be used to form the material. Since SPF is a process where the material is stretched, the part is not a uniform thickness when completed. A variation of the process combines SPF with diffusion bonding (SPF/DB) of two or more pieces of titanium together to produce integrally stiffened structure containing very few fasteners. The hot forming process uses matched metal tools, offset by the thickness of the starting material, are used to form the part contour at elevated temperature. The required part geometry usually contains no sharp features that have to be formed. Since the material is free to move as the die is closed, the part is fairly uniform in thickness when completed.

Abstract: An ultra-fine grained structure with an average size of ~ 1 μm was produced in a commercial Al–5.4%Mg–0.5%Mn–0.1%Zr–0.12%Si–0.014%Fe alloy by hot equal-channel angular pressing (ECAP) followed by isothermal rolling (IR). It was found that in the strain rate interval from 5.6×10^-4 to 2.8×10^-2 s^-1 the alloy exhibits a low-temperature superplasticity with elongation-to-failure exceeding 400% and the strain rate sensitivity coefficient of ~0.3. The highest elongation-to-failure of ~ 620% appeared at a temperature of ~ 275°C and an initial strain rate of ~ 5.6×10^-3 s^-1. The relationship between superplastic properties and microstructural evolution of the examined alloy is discussed.

Abstract: The superplastic behaviour of an Al-4.6%Mg-0.35%Mn-0.2%Sc-0.09%Zr alloy was studied in the temperature range 250-500°C at strain rates ranging from 10-4 to 10-1 s-1. The AA5024 was subjected to equal channel angular pressing (ECAP) at 300°C up to ~12. The highest elongation-to-failure of ∼3300% was attained at a temperature of 450°C and an initial strain rate of 5.6×10-1 s-1. Regularities of superplastic behaviour of the 5024 aluminium alloy are discussed.

Abstract: Traditionally the Aerospace Industry has, most often, selected heat treatable aluminum alloys for its sheet metal fairings, panels and skins. With the introduction of superplastic forming (SPF) in the late 70’s and early 80’s the initial applications of SPF aluminum utilized the heat treatable superplastic alloys that were available then (ie. 2004 and 7475). When superplastic 5083 alloy sheet became commercially available in the late 1980’s applications were focused on the ‘high end’ automobile and the European rail markets. More recently, the qualification of SP5083 to aerospace standards, combined with appropriate design criteria, has enabled an increasing number and variety of aerospace components to be Superformed from this non-heat treatable medium strength alloy. This presentation examines a number of recent aerospace applications of Superformed 5083; from contemporary tool designs through to finished components. The important attributes of both SPF design; the ability to create complex geometry, and the excellent post-formed characteristics of SP5083 that have created cost effective solutions to specific Aerospace Industry needs are illustrated. Future prospects for stronger 5000 series superplastic alloys are also discussed.

Abstract: SP 700 is a relatively new titanium alloy with superplastic properties improved over the industry standard, Ti 6Al-4V. In order to use this alloy in structural applications following superplastic forming, the mechanical properties need to be well understood. This paper will present a summary of both static and fatigue properties of SP 700 following simulated SPF and post processed conditions, and compare them to Ti 6Al-4V

Abstract: In this work authors present a study of the influence of the pressure profile on forming time and on post-forming characteristics of superplastically formed parts. Material parameters of an aluminium superplastic alloy (ALNOVI-U) were estimated on the basis of experimental tests and of a numerical approach. A numerical model of the forming process was then created and used for evaluating the pressure profile able to keep the maximum strain rate value close to a target value. Pressure profiles were calculated using a strain rate control algorithm, firstly following a conventional approach and monitoring the whole sheet, and then considering only the elements most deformed at the end of the forming process. Experimental results from different numerical pressure profiles are then compared, in terms post-forming characteristics, to test the effectiveness of the approach.

Abstract: This paper includes a review of the manufacturing technologies related to the combination of friction stir welding (FSW) and superplastic forming (SPF) to fabricate large monolithic titanium structures for aircraft. The particular focus is on the post FSW residual stress measured on the weld nugget after thermal treatments and SPF forming.

Abstract: Principles of fabrication of ultrafine grained bulk and sheet materials for superplastic deformation by the methods of multiple isothermal forging and warm rolling are formulated. New data on superplastic behaviour of commercial alloys, on diffusion bonding of similar and dissimilar materials, and superplastic forming of titanium alloys are presented. The recent application of the diffusion bonding and superplastic forming technology for the production of hollow blades is demonstrated.