How to etch a broken tap

When cutting threads in duralumin or aluminum, a mishap may occur and your tap will break, leaving a piece of debris inside the hole. Drilling tool steel out of duralumin-aluminum is incredibly difficult and means that the entire hole will be broken. There is a way in which the hole in the workpiece will remain intact, and the fragment can be removed without much difficulty.
The method is based on the difference in electrode potentials in different metals. In this regard, when aluminum (its alloys) come into contact with steel (iron), a galvanic couple is obtained. If such a pair is immersed in acid, galvanic corrosion of the steel will immediately begin.
Based on the size of a similar tap, you can estimate how deep the fragment lies.

Mark with a marker for clarity.

Everything is clearly visible under a microscope.

Needed for etching

Pack of citric acid powder 100 g.
Tap water 150-200 ml.
Utensils for pickling. I'll use stainless steel, but a regular enamel pan will work just fine.

Pour 2-3 teaspoons of citric acid into a cup and fill with water.

The electrolyte is ready.

Etching a piece of a tap in citric acid

Place the cup with the solution on the fire and lower the part with the broken tap into it.

Bring to a boil and reduce heat to minimum, but so that the liquid does not actively boil.

After 30 minutes.

After two hours of active etching.

We add water and acid, since the water boils away and the acid goes into the reaction.

After several hours, you can observe a black coating on the bottom of the dishes - the result of a chemical reaction.

Three hours passed and the tap was already noticeably burned.

After five hours of etching, nothing is visible in the groove.

We managed to extract the fragment of the tap by tapping.

The minutes were written down on a piece of paper, after which the condition was checked, plus water was added and citric acid was added.

With a similar tap you can see what happened to the fragment after the chemical reaction.

This is a simple, but quite time-consuming method. It’s good when the part is small in size and fits perfectly in a saucepan. It is more difficult when the part is massive.