Metallographic Features of Welded Joint of AMg6 + AMg6 Aluminum Plates after Explosion Welding

A method is selected for sample preparation and an etchant is chosen for high-contrast imaging of the microstructure of aluminum and welded joints of aluminum and its alloys obtained with the aid of explosion welding. The prepared microsections are initially etched using immersion in the Keller reagent (95 mL of water, 2.5 mL of nitric acid, 1.5 mL of hydrochloric acid, and 1 mL of hydrofluoric acid) for 15–20 s. Then, the samples are washed with water and dried. Generally, the microstructure is satisfactorily etched using such a procedure. However, contrast etching is not provided for a part of grain boundaries and, in addition, the nature of inclusions is not entirely clear. Longer exposures in the Keller reagent cause etching artifacts (etching pits and etching-out of single phase components, which complicates their further identification. For visualization of the nature of inclusions and higher-contrast etching, the samples (having been etched in the Keller reagent) are additionally etched in the Weck reagent (100 mL of water, 4 g of potassium permanganate, and 1 g of sodium hydroxide) using immersion of the sample for 20 s, washing with water, and drying. Sequential etching of aluminum alloys allows more contrast and clear visualization of the features of microstructure. The Keller reagent is recommended as the main etchant, and the additional Weck reagent provides coloring of several structural components.