Journal of Materials Research and Technology Journal of Materials Research and Technology
J Mater Res Technol 2018;7:66-72 DOI: 10.1016/j.jmrt.2017.05.006
Original Article
Precipitation hardening in dilute Al–Zr alloys
Pedro Henrique Lamarão Souzaa,, , Carlos Augusto Silva de Oliveiraa, José Maria do Vale Quaresmab
a Universidade Federal de Santa Catarina – UFSC, Campus Universitário João David Ferreira Lima, rua Delfino Conti, s/n, Trindade, Florianópolis – SC, CEP: 88040-900, Brazil
b Universidade Federal do Pará – UFPA, Campus Guamá, rua Augusto Corrêa, n° 01, Guamá, Belém – PA, CP 479, CEP: 66075-110, Brazil
Received 06 April 2017, Accepted 15 May 2017

The aim of this study was to investigate the effect of solute content (hipoperitectic Al–0.22wt.%Zr and hiperperitectic Al–0.32wt.%Zr) on the precipitation hardening and microstructural evolution of dilute Al–Zr alloys isothermally aged. The materials were conventionally cast in a muffle furnace, solidified in a water-cooled Cu mold and subsequently heat-treated at the temperature of 650K (377°C) for 4, 12, 24, 100 and 400h. Mechanical characterization was performed at room temperature, using a microhardness tester and microstructural characterization was carried out on a Transmission Electron Microscope – TEM. The observed microhardness values increased during isothermal aging, due to the precipitation of nanometer-scale Al3Zr L12 particles. Peak strength was achieved within 100h of aging. After aging for 400h, microhardness values presented a slight decrease for both alloys, thus indicating overaging due to the coalescence of precipitates. Microhardness values increased with solute content, due to the precipitation of a higher number density of finer precipitates. After 400h of heat-treating, coalescence was higher for the alloy with lower solute content and, also, the presence of antiphase boundaries – APBs, planar faults associated with the L12 to D023 structural transition, were observed. Comparing theoretical calculations of the increment in strength due to precipitation strengthening with experimental results, it was observed that their values are in reasonable agreement. The Orowan dislocation looping mechanism takes place during precipitation hardening for both alloys in the peak hardness condition.

Aluminum alloys, Age hardening, Precipitation hardening mechanisms, Al3Zr
J Mater Res Technol 2018;7:66-72 DOI: 10.1016/j.jmrt.2017.05.006