Microstructure modification of high magnesium Al-Mg alloys containing Zr, Sc and Er additions subjected to the extrusion process

The analysis of the microstructure of the Al-7 wt.% Mg alloy, and these alloys with the addition of Er with Zr and Sc with Zr were performed. The influence of the micro-alloying elements on the microstructure evolution in different states: as-cast, homogenised and extruded were analysed. Design/methodology/approach The microstructure and the Brinell hardness of the high magnesium Al-Mg alloys were investigated in as-cast and as-extruded states. Before and after the extrusion process, microscopic investigations were made using light, scanning, and transmission electron microscopy. Findings The obtained results indicate that the micro-alloying elements in AlMg7 alloy showed high resistance to recrystallisation after extrusion at 400°C. The base AlMg7 alloy was characterised by a partially recrystallised structure after the hot extrusion process. Moreover, it was found out that micro-alloying elements resulted in an increase in the Brinell hardness by approx. 15% in AlMg7 alloy after hot extrusion. Research limitations/implications The development of Al-Mg alloys with a high Mg content is stimulated by the desire to reduce the weight of the alloys by improving the strength of Al solid solution with Mg, as well as by the plastic working processes. Unfortunately, recovery and recrystallisation occur after plastic deformation processes due to the mobility of the grain boundaries, leading to remodelling of the metal structure and consequently decreasing its mechanical properties. One of the ways to inhibit the mobility of the grain boundaries of the deformed Al-Mg alloy is to introduce the micro-alloying elements which form thermally stable dispersoids. The obtained bars with appropriate mechanical properties can be used as a semi-finished product for the forging process to obtain a final product with high mechanical properties, which will be the subject of further research. Practical implications Extruded rods can be used as semi-finished products for cold forging to achieve products with complex shapes and high mechanical properties.Originality/value Conventional extrusion tests for Al-Mg alloys are extremely rare and limited to equal channel angular pressing (ECAP) and hydrostatic extrusion (HE). On the other hand, the recovery and recrystallisation processes which occurred in the AlMg alloys after hot extrusion led to the remodelling of the microstructure of the alloys and a decrease in their mechanical properties. The following study aims to analyse the microstructure of Al-7 wt.% Mg alloys containing additions of Sc and Zr, as well as Er and Zr, subjected to the conventional extrusion process at 400°C. This paper can complement knowledge about the recrystallisation resistance of AlMg alloys after a conventional extrusion process.