19/03/2014. Research In Focus. Microstructural Control for Optimized Formability

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1 Conquering low formability for optimized microstructures Dr João Fonseca Conquering Low Formability for optimized microstructures Key Objectives AIM: Advance understanding and predictive modelling to enable energy efficient, cost effective routes for forming of light alloys with poor formability Improve understanding of deformation mechanics in HCP metals - e.g. Ti, Mg, - allowing implementation in crystal plasticity models. Develop models for microstructure control during thermomechanical processing to achieve highly formable microstructures Capture the influences of microstructural and texture heterogeneities that cause strain localisation and limit formability e.g. impact of recycling Extend modelling to advanced warm forming processes and other novel approaches to increase formability LATEST2 formability resources 4 Academics 2 PDRAs 9 PhD Students 7 CDT PhD Students 2 EngD Student MSc Students 8 Technicians 4 Visiting Scientists Formability: Research overview Microstructure control for improved formability Understanding recrystallization in Al alloys (PSN) Mechanics of deformation around particles Understanding recrystallization in Mg alloys Understanding the formability of difficult to form light alloys Formability of high strength Al alloys Modelling formability in Ti and Mg alloys Advanced Layer Manufacturing Microstructure control Micromechanics of ALM structures Effect of forming on performance Forming affects fatigue performance Forging affects corrosion behaviour Formability: Expertise overview Experimental Micromechanics In-situ studies using HRDIC EBSD analysis of texture, microtexture and the deformed state Plasticity modelling Crystal plasticity modelling Deformation texture Miromechanics Twining slip interactions Formability testing Cold and warm formability testing Non-contact strain measurement Research In Focus Microstructural Control for Optimized Formability 1

2 Microstructural control understanding PSN Thomas Hill, Liam Dwyer Collaborators Novelis PSN efficiency is not well understood Effect of PSN on texture is sometimes unpredictable Size of particle affects efficiency and local s (texture) Use HRDIC to measure strain and lattice Need sub-micron resolution Need nanometre-sized speckles Gold remodelling gives a spatial resolution of nm Improvement in resolution: gold remodelling 4 VECTORS PER μm 2, VECTORS PER μm 2 Need to study deformation in plain strain Deformation at the surface is different from deformation in the bulk The PDZ development needs to be studied in plain strain Al-Si PTFE film Local strain evolution Strain heterogeneity -% ε yy -% % 28% 2

3 Slip band alignment results HRDIC results -% Compressive strain -% % Measured - - HRDIC results EBSD Misorientation decomposition Rotation around RD Measured - Misorientation with respect to starting orientation - - Rotation around TD - Rotation around ND Back scattered imaging EBSD Misorientation decomposition Rotation around RD Misorientation with respect to mean orientation DIC - Rotation around TD - Rotation around ND EBSD - -

4 -% CPFEM modelling of Particle Deformation Zone Cube oriented grain -% DIC strain % 1o HRDIC CPFEM 5o EBSD o -5o -1o CPFEM modelling of Particle Deformation Zone Solution heat treated material S oriented grain CPFEM HRDIC Al Effect of Increased Recycled Content on AAxxx Sheet Thomas Hill, Liam Dwyer Collaborators Novelis Torsion testing to generate high strain/strain rate deformation (collaboration with University of Sheffield) Quantitative particle analysis to compare with model predictions Model alloys developed to study effect of systematic variation in Fe, Mn, Si content view system used to study effect of composition/processing on distribution of constituents and dispersoids in D (with GET) Effect of deformation on particle evolution studied Models developed for particle evolution during rolling Link to CPFEM model for deformation zones formed around constituents using realistic particle shapes Work contributing to Novelis Through Process Modelling collaboration 4

5 Effect of Rare-Earth Elements on Formability of Mg alloys David Griffiths (Phd CDT) Collaborators Magnesium Electron Forming limit diagram RE additions improve low T formability of Mg alloys RE modifies strong basal texture in Mg BUT improvement for biaxial conditions is less than uniaxial Texture evolution: Cold Rolling 1 st reduction 2 nd reduction rd reduction 1 DD Origin of texture modification unclear Factors determining critical minimum RE content not understood Related to solubility? Atomic misfit? Binary Mg-RE produced to test hypotheses Rolled AZ1 Non-RE Alloy Rolled ZEK RE Alloy 2x 5x 7x Strong normal basal fibre texture after cold drawing No evidence for shear banding Microstructure control in Mg alloys RE additions David Griffiths, Mark Chatterton Collaborators MEL 1 DD Cold draw WE4 extrusion (very weak starting texture), passes up to ε T =.7 Anneal, 1h 44 C to recrystallize 1-1 Starting extrusion RE Effect - Summary Evidence RE strongly suppress boundary migration during hot deformation Texture weakens on static recrystallization with or without RE Cold drawing of WE4 and recrystallization weakens texture but no strong RE peak Enables Interpretation greater stored energy and more orientation heterogeneity to be retained prior to annealing/srx In dilute Mg-RE, weaker texture may result from DRX suppression alone. Texture of ZEK not explained by this Unrecrystallized shear bands/heterogeneities formed by rolling/extrusion prior to annealing are essential to form distinct RE peak Research In Focus Conquering low formability in light alloys Warm forming of high strength aluminium automotive alloys Ross Nolan Collaborators Costellium The aim is to enable the use of high strength (aerospace) alloys in automotive applications Characterise formability (FLD) Overcome poor formability -> warm forming Understand physical mechanisms limiting formability Particle distribution Deformation and recovery mechanisms (effect of temperature) 5

6 721 effect of temper on tensile properties 2 Elevated Temperature Deep Drawing tests 721-T4 2 True Stress /MPa T4 C 17 C 19 C True Stress/MPa 22 C T 2 C True Strain 17 Hardness Vickers 1 T T Temperature / C True Strain True Strain Temperature / C 19 C RT 22 C 2 C Impact on corrosion behaviour? Formability of hcp alloys (Ti, Mg) Why low formability? High R ratio doesn t help Good ductility in uniaxial deformation Formability of Ti better than Mg Important to have a fine grain size and a near random texture CPFEM modelling of hcp deformation Added twinning to crystal plasticity formulation Texture predictions are good What affects strain localization? Twinning shear Twinning reorientation Twinning modes Availability of basal/prismatic slip Effect of biaxial versus uniaxial loading Effect of texture strengthening Mg formability limited by twinning? Microstructure Evolution by Nakazima Strip Tests AZ1B O AZ1B O Away from fracture tip At fracture tip Extension Twins Double Twins HAGB >15 LAGB <2 Twinning and localised twin-bands formation in strip specimens Using Precipitates to Control Twinning Joe Robson, Chuleeporn Pai-Rai Collaborators Magnesium Elektron Effect of Aluminium on mechanical behaviour of Ti Arnas Fitzner, Michael Preuss Collaborators TIMET - σ -1 in MPa -9 µm Uniaxial compression Quasi static, 1*1-1/s Room temperature Loading in RD Plate shaped precipitates in AZ91 strongly reduce mechanical asymmetry in extrusion FE model to predict plastic relaxation around precipitate in twin TEM micrograph showing deflection of a plate shaped precipitate embedded in a twin in AZ91 Precipitates of correct shape and habit can strongly reduce mechanical asymmetry in Mg alloys by preferentially suppressing twinning Models develop to demonstrate origin of this effect and identify optimum precipitate characteristics Collaboration with Deakin University, Australia Ex-situ characterisation of microstructure and texture Optical microscopy Electron microscopy: EDX, BSE, EBSD In-situ characterisation - of lattice strains by neutron diffraction ε in mm/mm 7/1/21 Arnas Fitzner

7 Neutron diffraction at Engin-X Development of twin fraction in Ti-Al Arnas Fitzner, Michael Preuss Collaborators TIMET axial ε [%] Ti-Al Ti-2Al Ti-4Al Ti-4Al aged Ti-Al Ti-Al aged Ti8Al Ti-Al Starting point: Twin nucleation Slope: Twin growth rate 9 Time of flight in µs ε [%] 9 {} {11} {2} {12} 4 {11} {1} Sample I{2} axial [µa] 8 Neutron counts /µs µε{2} transverse [µm/m] Transvers e I{2} axial [µa] ε [%] Understanding formability using CPFEM Strain localisation, twinning and stress state Predicted texture evolution during forming (weak starting texture) Twinning causes fast texture changes during forming Uniaxial (15%) Biaxial (5%) There are near neighbour effects on twinning Summary Significant formability activity in LATEST2 Developing fundamental understanding of what underpins formability in light alloys Combination of advanced analytical techniques and plasticity modelling to understand formability Most of the work is funded by industry: Novelis, Constellium, Rolls-Royce, Westinghouse, Airbus, BAE systems, Otto-Fuchs, Timet, Nippon Steel, EdF and AMEC Link to work on bulk formability on Nickel alloys, Zirconium alloys, Stainless Steel, Titanium alloys 7