Precipitation Evolution in the Heat‐Affected Zone and Coating Material of AA2024 Processed by Friction Surfacing

Abstract

Herein, self‐mating coating depositions are generated from Al–Cu–Mg alloy AA2024 by using the solid‐state joining method, friction surfacing (FS). The precipitation evolution in the heat‐affected zone (HAZ) of the substrate material and in the deposited coatings is analyzed using hardness mapping, temperature measurements, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) as well as synchrotron small‐angle X‐Ray scattering (SAXS) used for mapping mean particle radius and particle volume fraction over the whole sample. Quantitative measurements of the thermal cycle using thermocouples positioned inside the substrate sheets reveal a distinguishing temperature distribution and a maximum temperature up to 420 °C close to the center of the bonding zone (BZ). The hardness distribution is frequently encountered in solid‐state joining processes. It can be understood taking into account the complex modifications of the precipitate size distribution, including small Guinier–Preston–Bagaryatsky GPB (Al2CuMg)/Guinier–Preston GP(I) (Al2Cu)‐zones and larger S′ (Al2CuMg)/θ′ (Al2Cu)‐phases. Uniform precipitation of small and larger particles leads to an increase in hardness. It has become apparent that the highest hardness values within the HAZ are obtained when the volume fractions of small and larger particles are increased and equally distributed.