Ola Jensrud

The development of microstructures in AlLi alloys

Abstract The nucleation, growth and coarsening of precipitates of an AlLi alloy were investigated. The equilibrium phase AlLi nucleates on grain boundaries, while the coherent and metastable Al3Li nucleates homogeneously within the matrix grains. Isothermal aging resulted in the growth of Al3Li precipitates. The growth process was dependent on the cube root of the time. Together with the growth of the matrix precipitates, a preferential coarsening of the AlLi precipitates on the grain boundaries occurred. To accommodate the accelerated growth in the grain boundary regions a precipitate-free zone (PFZ) developed. The change in the PFZ width was a function of the square root of the time. The AlLi solvus was redetermined metallographically at three temperatures, the values corresponding closely to the AlLi solvus values given in the literature. From the coarsening experiments the product of the coefficient of diffusion and the interfacial free energy of the precipitates was found. The coefficient of diffusion was determined independently by measuring the PFZ growth rate.

Cold forging of high strength aluminum alloys and the development of new thermomechanical processing

Abstract Cold forging is a process suitable for manufacturing low-cost and high quality automotive components in high strength aluminium alloys. This method is particularly suitable for parts with narrow geometrical tolerances, good concentricity, smooth surface finish and for near net shape products. However, an increasing request for producing components at a lower cost requires even more economical production processes. Forming in the warm condition is an alternative process that has the advantages of producing rather complicated geometrical shapes in less operation steps compared to cold forming. In addition, warm forming at moderate temperatures has all the benefits of cold forming including good control of the microstructure and thereby improved strength and ductility.

Selection of aluminium alloys for extrusion profiles: methodology and development of a specialised software

Material selection methods are applied to the selection of extruded aluminium alloys components. The competition between materials cost and processing cost in relation to materials extrudability and shape complexity is investigated. A tailored software for industrial purposes has been developed.

Characterization of microstructure and strain response in Ti−6Al−4V plasma welding deposited material by combined EBSD and in-situ tensile test

Abstract Additive layer manufacturing (ALM) of aerospace grade titanium components shows great promise in supplying a cost-effective alternative to the conventional production routes. Complex microstructures comprised of columnar remnants of directionally solidified β -grains, with interior inhabited by colonies of finer α -plate structures, were found in samples produced by layered plasma welding of Ti–6Al–4V alloy. The application of in-situ tensile tests combined with rapid offline electron backscatter diffraction (EBSD) analysis provides a powerful tool for understanding and drawing qualitative correlations between microstructural features and deformation characteristics. Non-uniform deformation occurs due to a strong variation in strain response between colonies and across columnar grain boundaries. Prismatic and basal slip systems are active, with the prismatic systems contributing to the most severe deformation through coarse and widely spaced slip lines. Certain colonies behave as microstructural units, with easy slip transmission across the entire colony. Other regions exhibit significant deformation mismatch, with local build-up of strain gradients and stress concentration. The segmentation occurs due to the growth morphology and variant constraints imposed by the columnar solidification structures through orientation relationships, interface alignment and preferred growth directions. Tensile tests perpendicular to columnar structures reveal deformation localization at columnar grain boundaries. In this work connections are made between the theoretical macro- and microstructural growth mechanisms and the observed microstructure of the Ti–6Al–4V alloy, which in turn is linked to observations during in-situ tensile tests.

Cold forging and grain size control in an Al-1.2wt%Si alloy

Abstract The axis-symmetrical version of the simulatin program FORGE2® has been used to simulate forward and reverse cold extrusion in an Al-1.2wt%Si alloy. The simulations have been validated by experimental tests accomplished in an 800 metric tons laboratory press equipped with an external high resolution load transducer ranging from 0 to 100 KN. Constitutive data for the Al-1.2wt%Si alloy has been determined by compression tests at temperatures between room temperature and 250°C at strain rates of 0.1 s−1, 1 s−1 and 4 s−1. The temperature development has been simulated and the result is in good agreement with experimental data obtained by measuring the temperature in the workpiece during forming. A correlation between the strain distribution after forming and the grain size after subsequent annealing has been established.

High Strength Aluminium Alloys Extrusions - A Review of the Thermo-Mechanical-Process in High Performance Profile Manufacturing

High strength aluminium alloys extrusions have successfully been applied for years in transportation industry. High strength alloys are normally understood to be alloys based on the Al-Mg-Zn system (7xxx) with addition of Cu in some cases and of course some micro structural controlling elements as Cr or Zr. The level of strength in the hardened condition (T6) is typical in the range from 320 to 500 MPa. The combination of strength and ductility of extrusions from the 7xxx series alloy gives several advantages in light weight construction and can contribute to lighter body and chassis in automotive. Significant improvements in extrusion speed are realized when the ratio Zn/Mg is increasing this means that alloys with high Zn and low Mg like 7108 and 7003 are favourable. Zr is the most promising element with respect to control the recrystallization phenomena. The fully understanding chemistry and the thermo-mechanical process route in profile based components manufacturing is concluded to be fundamental for high performance products.

Through Process Prevention of Recrystallization in Hot Formed Aluminium Structural Car Components

Aluminium is increasingly used in structural components in cars. The advantages are many, and recyclability, weight saving and energy absorption during impact and are often considered as the most important. There are also several disadvantages compared to iron and steel, i.e. material cost, low stiffness, lack of fatigue limit, high thermal conductivity, high thermal expansion coefficient, corrosion susceptibility and others. To enhance the advantages and to minimize the disadvantages, several actions can be made. To prevent recrystallization is one of them, and has to be dealt with from the melt through all thermo-mechanical, mass reducing and assembly processes – “from the ore to the car”. As recrystallization may reduce the static strength and fatigue life time in a finished component considerably, preventing recrystallization is as important as to optimize component geometry. Additionally, there is considerable risk of inter-granular cracking or melting during thermo-mechanical processing, especially those involving very high strain and forming temperatures above eutectics. To prevent recrystallization, a well balanced budget on chemical composition, strain, strain rates and temperatures is essential. Examples of successes and failures are vital ingredients of the base of knowledge in development of highly utilized aluminium car components. All process steps, from alloying and melt treatment of wrought aluminium alloys to the assembly of a finished component, can influence on product performance. AlMgSi1 alloys are used as examples in evaluating recrystallization in this paper. By focusing on recrystallization, other major factors influencing performance are not neglected, but not further discussed here.

Improved Extrudability of High Strength Alloys Using an Optimization Method Based on a Combination of Experiments and FEM Software

Numerical analysis of the material flow during the extrusion process for high alloyed variants of the AA 6xxx series is presented in this paper. The analysis was performed by using the commercial FE code Forge2011®. Another issue considered in the paper was an interrelation between the die geometry and the critical extrusion process variables. For optimization of the die exit geometry, the model was produced with the use of linked equation in SolidWorks® combined with Mode FRONTIER. Several extrusion trials were performed to provide a basis for the verification of simulation results as extrusion temperature, speed and force. For the purpose, rods of a model alloy designated as AlMgSi4, based on an industrial AA6082 aluminium alloy with significantly higher silicon content, were extruded. A good correlation between measured and calculated results was obtained. This approach may enable simplifying when dealing with design of a new alloy.

A new tribological system test for integrated hot forming and die quenching of aluminium alloy sheets

The automotive industry is searching for alternative powertrain and lightweight solutions to meet steadily stricter emission standards and regulations. To leverage the use of high-strength age-hardening aluminium alloys, new processes such as hot forming and in-die quenching are under development in a number of different groups. 0ne of the challenges with in-die quenching is controlling the friction regime stability due to rapidly changing temperatures at both the tool and the blank surfaces under complex deformation modes. In this paper, a cup-based test method is developed and tested for combinations of draw ring materials and lubricants on AA6070 aluminium sheets. Qualitative investigations of formed cups indicate reduced adhesion of aluminium at the tool surface can be obtained by choosing the right combination of tool and lubrication parameters. A correlation between maximum punch force, formed cup height and average Coulomb friction coefficient is observed in both physical experiments and forming si...