Gradient phase transformation of Al–Zn–Mg–Cu alloy induced by nonlinear interface wetting under electromagnetic shocking treatment.

A novel electromagnetic shocking treatment (EST) was put forward to selectively embellish interface microstructure of solid alloy and improve its performance in our previous work. However, considering the nonlinear response characteristic of phase evolution under EST, the effect of precipitates evolution on precipitate and microhardness distribution of Al7075-T73 alloy is worth of attention and still unknown. Herein, microhardness distribution test and TEM characterization of precipitates for Al7075-T73 alloy are carried out to explore the influence mechanism of EST on the precipitate and microhardness distribution. Compared with the received sample, the microhardness distribution turns more homogeneous, while the average microhardness remains basically constant for EST sample. Besides, for EST sample, grain boundary precipitates (GBPs) dissolve and coarsen obviously, while there also exists that the distribution of matrix intragranular precipitates remains basically constant with that of the received sample. Meanwhile, stripy grain boundaries (GBs) can be observed more commonly and GB wetting occurs for EST sample. It indicates that EST promotes nonlinear interface wetting and results in nonlinear phase transition, inducing significant GBPs transformation and then gradient phase transition of precipitates within grain size scale. The resultant gradient phase distribution combined with nonlinear interface bridging promotes a more homogeneous microhardness distribution without losing the mechanical properties of aluminum alloy. This work provides a new understanding about the effect of EST on the microstructure evolution process of solid alloy and is beneficial to the optimization of EST process to improve the service performance of alloys and even finished parts. [ABSTRACT FROM AUTHOR]