Hexagonal close-packed (hcp) metals show a deformation behavior, which is quite different from that of materials with cubic crystalline structure. As a consequence, rolled or extruded products of magnesium and its alloys exhibit a strong anisotropy and an unlike yielding in tension and compression. In this work, the microstructural mechanisms of deformation in pure magnesium are modeled by visco-plastic constitutive equations of crystal plasticity. Single crystals and textured polycrystals are analyzed numerically. By means of virtual mechanical tests of representative volume elements mesoscopic yield surfaces are generated. The linking of micro-and mesoscale provides a procedure for the simulation of the yielding and hardening behavior of arbitrarily textured solids with hcp structure such as extruded bars or rolled plates.

Anomalies in the mechanical behaviour of magnesium like anisotropy and strength mismatch originate from its hexagonal close-packed (hcp) crystallographic structure. Hcp metals hold a reduced number of available slip systems compared to body-centred cubic (bcc) and face-centred cubic (fcc) lattices, making plastic deformation more difficult. With the asymmetric distribution of slip systems over the crystallographic reference sphere, various primary and secondary slip and twinning mechanisms can and have to be activated at the same time. Understanding the mechanisms of dislocation gliding and deformation twinning for single crystals and polycrystalline aggregates constitutes the foundation for modelling of the macroscopic mechanical behaviour. To this end, microstructural experimental observations, mechanical tests and numerical modelling are combined.Channel-die compression tests on Mg single crystals for various crystallographic orientations and on textured and polycrystals have been conducted by Kelley and Hosford. [1,2] Their data are used to identify the parameters of a crystal plasticity model. The model is then applied for predicting the mesoscopic deformation of polycrystalline representative volume elements (RVEs). In this way the microscopic features developing during plastic deformation of Mg are linked to the mesoscale and allow for predicting the yielding behaviour of arbitrarily textured solids, for example rolled plates.Due to limitations in computational power, simulations of the behaviour of macroscopic structures cannot be performed effectively based on models of crystal plasticity. They require constitutive equations to be used in the framework of phenomenological plasticity, i.e. a plastic potential and a flow rule. The presented method can be used to calibrate parameters of any plastic potential. Here, the plastic potential proposed by Cazacu and Barlat [3] is used for the simulation of a cup-forming process.

In virtual design of the hot stamping process, a reliable description of the material flow behaviour is an important input to ensure accurate estimations of the parts feasibility. Currently, to characterise the hot stamping material’s flow behaviour at elevated temperatures, tensile and upsetting tests are available. The measurement of the flow behaviour out of such tests, which is generally temperature and strain rate dependent, still remains a complex task. Therefore traditional methods to measure flow curves out of such measurements are not necessarily precise enough. In this contribution the authors focus on non-isothermal conductive tensile tests of the manganese-boron steel MBW® 1500 in order to understand its flow behaviour at elevated temperature. Numerical calculations using Finite Element Method (FEM) of the tests itself with correct boundary conditions as well as for all necessary phenomena are used to identify accurately the material’s flow curves by use of inverse optimisation. Finally, for validation purpose the identified flow curves out of the optimisation method were used to simulate the hot stamping of two different parts. Both geometries were chosen such that various strain paths are covered i.e. uniaxial tension to plane strain.

A crystal plasticity model has been used to simulate channel die experiments on both, pure magnesium single crystals and polycrystalline textured rolled plates. Deformation mechanisms and slip system activity can be identified by FE-analyses of single crystals. The role of twinning can be understood and modeled phenomenologically by an additional slip system. Simulations of polycrystalline aggregates are used to obtain a representation of the material's phenomenological yield function in order to describe the plastic deformation behavior using the framework of continuum mechanics. This allows for accounting for the specific texture and thus for its optimization. The tension- compression asymmetry, which is typical for mechanically processed magnesium material, can be reproduced by means of the crystal plasticity and a phenomenological model.

Hot stamping steels are trending towards increased ductility without sacrificing too much stiffness. Thus a new aluminum silicon coated grade, MBW 1200 + AS has been developed, with typical yield strength after hot stamping and paint baking of YS ≈ 1000 MPa, tensile strength TS ≈ 1200 MPa and A80 > 5.0 %. The highly increased ductility compared to 22MnB5 expresses through the particularly increased bending angle of >75° and the logarithmic true thickness strain of ≈0.90. Hence MBW 1200 shows the desired significantly higher ductility compared to 22MnB5 in lateral crash testing without crack appearance. The process stability has been approved by different tests, e.g. increased furnace dwell time, tool temperature and transfer time. Verifying MBW 1200 in patchwork blank applications with total thicknesses of 3.0 and 3.5 mm showed only a minor decrease of YS and TS between 30 and 50 MPa and leaves the Vickers hardness at ≈400 HV10 with fully martensitic microstructure. In partial press hardening tests, using tools heated of up to 550 °C, bending angles reach the test’s maximum and YS falls below 500 MPa with a hardness of ≈210 HV1. Finally in a comparison between experiment and numerical hot stamping simulation it can be shown, that the determined material modelling parameters can well be used in the feasibility analysis of new automotive components.