A01 – Solid Solution Effects on the Slip System Selection and Dislocation Activity

PIs: Stefanie Sandlöbes-Haut (IMM), Dierk Raabe (MPIE)

SFB researcher: Wassilios Delis (IMM)

Main goal of project A01 is the investigation of one- and two-dimensional defect phases, such as dislocations and stacking-faults, in lean alloyed Mg-Al-Ca wrought alloys with respect to their local chemistry and structure and their effect on the mechanical properties.

For this purpose, seven different ternary Mg-Al-Ca alloys, one Mg-Ca alloy and one Mg-Al alloy in the solid solution regime were synthesised in project S. A first screening of the mechanical properties by tensile and compression loading was performed to detect property changes indicating a change of defect phases. A parallel screening approach using combinatorial thin films from project B02 was performed by nanomechanical testing. These tests reveal that indeed only for the ternary alloys a significant increase in ductility is observed. Further, the microstructures were evaluated to measure grain sizes, textures and analyse if precipitations occur. It can be seen that Ca leads to a decrease of the grain size and all alloys within or near the solubility limit are solid solutions. The two crucial deformation-controlling mechanisms, the activation of slip systems and the present textures were investigated. The first, by slip line analysis and the latter by XRD. The slip line analysis shows an increased activation of non-basal <c+a> slip with increasing amount Al. The texture is weakened by Ca with respect to the amount of solute atoms and their solubility.

In addition, the texture development during cold rolling was investigated to get insights into the activated deformation systems.

Based on the results of the slip line analysis and the texture evolution, micropillar compression was performed to calculate the critical resolved shear stresses (CRSS). The basal CRSS shows a dependency to the Al:Ca-ratio. Here, TEM investigations were conducted to identify the activated slip systems stacking faults and visualise the present defect phases in this controlled deformation state. High amounts of both non-basal dislocations and stacking faults are present, especially in the vicinity of grain and twin boundaries.

APT in cooperation with project B03 is used to look deeper at slip lines and their chemistry and HR(S)TEM in project A03 is used to resolve the defect phase structure at the atomic scale.

Finally, the results are connected to describe the deformation mechanisms and ductility descriptors.