Microstructural Evolution and Hetero-Deformation-Induced Strengthening in Surface-Bulk Hierarchical Al-Mg-Sc-Zr (A5xxx) Alloys Processed by ECAP and Shot Peening

• Applicant: Professor Dr.-Ing. Martin Franz-Xaver Wagner
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 575728112

This project aims to elucidate the fundamental mechanisms driving hierarchical microstructure development and hetero-deformation-induced (HDI) strengthening in a thermally stable Al-Mg-Sc-Zr alloy subjected to combined Equal Channel Angular Pressing (ECAP) and shot peening. This alloy is specifically chosen for its solid solution strength and coherent Al₃(Sc,Zr) dispersoids, which suppress abnormal grain growth during severe plastic deformation. These characteristics enable the design of gradient structures with well-controlled microstructural and mechanical heterogeneity. For the first time, ECAP and shot peening are combined in this alloy system to produce complementary gradients in grain size, dislocation density, residual stress, and strain. The central hypothesis is that bulk-surface gradient architectures activate HDI strengthening mechanisms via the accumulation of geometrically necessary dislocations, generation of long-range back stresses, and enhanced strain partitioning. The project addresses a critical knowledge gap: how does the interplay between internal ultrafine grains and surface-imposed strain gradients control interface stability, plasticity, and crack initiation in heterostructured aluminum alloys? Conventional strengthening models overlook the role of heterogeneous interfaces, strain incompatibility, and gradient-induced dislocation structures. This project seeks to decouple these variables by systematically varying ECAP routes, peening intensity, and heat treatment conditions tailored to the Al-Mg-Sc-Zr system. A correlative, multiscale characterization approach is central to the methodology. Electron back-scatter diffraction will map grain size gradients, local misorientations, and substructure formation. X-ray diffraction will provide depth-resolved residual stress profiles. Nanoindentation mapping will quantify hardness and modulus gradients, while transmission electron microscopy will reveal dislocation structures, particle–matrix interfaces, and dynamic recrystallization phenomena at surface and bulk regions. These datasets will be correlated to elucidate mechanisms underlying HDI plasticity and their spatial evolution across the gradient. The project comprises five interconnected work packages: (1) alloy synthesis and ECAP with varying routes and passes; (2) shot peening under controlled intensities and durations; (3) multiscale microstructural and residual stress analysis; (4) mechanical testing and HDI mechanism quantification; and (5) integration of experimental findings into a mechanistic design framework. By combining gradient-inducing bulk and surface processing with advanced microscopy, the project will establish transferable strategies for designing ultrafine-grained, thermally stable aluminum alloys. The insights gained will expand the knowledge on strain-gradient plasticity and support the development of high-performance heterostructued metals with enhanced strength-ductility synergy and damage tolerance.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Cagatay Elibol
• Cooperation Partner: Professor Dr. Egemen Avcu