Аbout the possibility of annealing to relieve internal stresses in gilded brass products made of sheet brass by deformation

The article examines the possibility of annealing to relieve internal stresses in the objects of the collection of gilded church utensils made of sheet brass using cold deformation. The composition of products and coatings, their manufacturing technology, and the level of internal stresses were determined on the samples taken from them using x-ray fluorescence method, scanning electron microscopy, metallography and microhardness measurements. It was found that the objects were made of brass, similar in composition to the L66 and L68 brands, their microstructure is distinguished by large recrystallized grains, along the boundaries of which intercrystalline cracks spread. The cause of such destruction is internal stresses, which also provoke intercrystalline corrosion, accompanied by the formation of copper oxide in the form of layers and individual inclusions at the grain boundaries. Gilding was applied to the products using the amalgam method, in two objects it was imitated using a yellow varnish located on a layer of amalgam silvering. The coatings are characterized by a small thickness, the values of which vary in different areas within 0.5-3 microns, metal breaks are noticeable in them, sometimes a fragmented structure is observed. Defects in coatings contribute to the development of corrosion, so they must be protected using reliable conservation methods. Annealing of samples in the temperature range of 300-500°C for 2 hours showed that internal stresses almost completely disappear at 500°C. Annealing at all temperatures used does not cause diffusion of gold and silver from the surface deep into the samples. Brass products with a gilded or silver-plated surface can be annealed to relieve internal stresses at a temperature of 500°C. The duration of annealing can be reduced from 2 hours to 15-30 minutes.