What is metal aging?
Metal aging is one of the common methods of changing the properties of metal alloys. While the properties of many metals may be changed by heating, quenching or work hardening, some metal alloys are specially formulated to age. Aging can change the physical and aesthetic properties of the alloy, giving it distinct characteristics from the unaged form.
What is Metal Aging?
Metal aging is a process used to dissolve heat treat metal alloys and can be done artificially or naturally. Natural aging occurs throughout the lifetime of a metal alloy. During natural aging, supersaturated alloying elements in metal alloys form so-called metallic precipitates. These precipitates hinder dislocations in the metal, increasing the strength and hardness of the metal alloy while reducing its ductility.
Artificial aging is a process that accelerates the formation of precipitated phases in the heat-treated metal alloy solution, and its speed is much faster than the natural aging process. The artificial aging process is carried out by raising the temperature of the solution heat treated metal alloy to a temperature below its recrystallization temperature but sufficient to accelerate the formation of precipitated phases. Once the alloying element precipitates have become the correct size, the metal alloy is cooled rapidly to prevent any further changes in the metal precipitates.
What types of metals can age?
Aluminum : The 2XXX, 6XXX, and 7XXX series of aluminum alloys are all ageable and derive their strength in many different forms from artificial aging. One of the common aged aluminum alloys is 6061-T6. It has magnesium silicide precipitates, which block dislocations in the form of -T6, and greatly increase its strength and hardness. Stainless Steel: 17/10P, 17/4PH and 17/7PH are several common stainless steel alloys that, when properly aged, are extremely strong and hard due to the metal alloy precipitation in their structure.
Copper alloys : C17200 and C17300 are two copper-beryllium alloys commonly used in industry. Copper is generally known for being soft and ductile, and when used with the proper addition of alloying elements and proper aging techniques, copper can be quite hard, strong and brittle.
Other metal alloys : Titanium, nickel, magnesium, and several other metals can be aged if they contain alloying elements in their chemical composition. When metal alloys age, whether naturally or artificially, one problem is so-called overaging. This occurs when the size of the precipitated phases changes due to the aging process being carried out beyond the application's vantage point. This usually results in a reduction in strength and hardness. Two common methods are welding or cold working the metal.
Care should be taken to determine if solution heat treated metals need to be artificially aged again, following either of these two processes to ensure the desired mechanical properties are still present.
