Precipitation hardening, or age hardening, provides one of the most widely used mechanisms for the strengthening of metal alloys. The fundamental understanding and basis for this technique was established in early work at the U. S. Bureau of Standards on Duralumin. The importance of theoretical suggestion for the development of new alloys is clear from the historical record. At the end of the 19th century, cast iron was the only important commercial alloy not already known to western technology at the time of the Romans. When age hardening of aluminum was discovered accidentally by Wilm, during the years 1903 -1911, it quickly became an important commercial alloy under the trade name Duralumin. The strength and hardness of some metal alloys may be enhanced by the formation of extremely small uniformly dispersed second-phase particles within the original phase matrix in a process known as precipitation or age hardening. The precipitate particles act as obstacles to dislocation movement and thereby strengthen the heat-treated alloys. Many aluminum based alloys, copper- tin, certain steels, nickel based super-alloys and titanium alloys can be strengthened by age hardening processes. In order for an alloy system to be able to be precipitation-strengthened, there must be a terminal solid solution that has a decreasing solid solubility as the temperature decreases. The Al-Cu (Duralumin is an aluminum alloy of 2XXX group) phase diagram shown in Figure 1 shows this type of decrease along the solvus between the and + regions. Consider a 96wt%Al – 4wt%Cu alloy which is chosen since there is a large degrease in the solid solubility of solid solution in decreasing the temperature from 550°C to 75°C. Solution Precipitation hardening, or age hardening, provides one of the most widely used mechanisms for the strengthening of metal alloys. The fundamental understanding and basis for this technique was established in early work at the U. S. Bureau of Standards on Duralumin. The importance of theoretical suggestion for the development of new alloys is clear from the historical record. At the end of the 19th century, cast iron was the only important commercial alloy not already known to western technology at the time of the Romans. When age hardening of aluminum was discovered accidentally by Wilm, during the years 1903 -1911, it quickly became an important commercial alloy under the trade name Duralumin. The strength and hardness of some metal alloys may be enhanced by the formation of extremely small uniformly dispersed second-phase particles within the original phase matrix in a process known as precipitation or age hardening. The precipitate particles act as obstacles to dislocation movement and thereby strengthen the heat-treated alloys. Many aluminum based alloys, copper- tin, certain steels, nickel based super-alloys and titanium alloys can be strengthened by age hardening processes. In order for an alloy system to be able to be precipitation-strengthene.

1. Precipitation hardening, or age hardening, provides one of the most widely used mechanisms for
the strengthening of metal alloys. The fundamental understanding and basis for this technique
was established in early work at the U. S. Bureau of Standards on Duralumin.
The importance of theoretical suggestion for the development of new alloys is clear from the
historical record. At the end of the 19th century, cast iron was the only important commercial
alloy not already known to western technology at the time of the Romans. When age hardening
of aluminum was discovered accidentally by Wilm, during the years 1903 -1911, it quickly
became an important commercial alloy under the trade name Duralumin.
The strength and hardness of some metal alloys may be enhanced by the formation of extremely
small uniformly dispersed second-phase particles within the original phase matrix in a process
known as precipitation or age hardening. The precipitate particles act as obstacles to dislocation
movement and thereby strengthen the heat-treated alloys. Many aluminum based alloys, copper-
tin, certain steels, nickel based super-alloys and titanium alloys can be strengthened by age
hardening processes.
In order for an alloy system to be able to be precipitation-strengthened, there must be a terminal
solid solution that has a decreasing solid solubility as the temperature decreases. The Al-Cu
(Duralumin is an aluminum alloy of 2XXX group) phase diagram shown in Figure 1 shows this
type of decrease along the solvus between the and + regions. Consider a 96wt%Al – 4wt%Cu
alloy which is chosen since there is a large degrease in the solid solubility of solid solution in
decreasing the temperature from 550°C to 75°C.
Solution
Precipitation hardening, or age hardening, provides one of the most widely used mechanisms for
the strengthening of metal alloys. The fundamental understanding and basis for this technique
was established in early work at the U. S. Bureau of Standards on Duralumin.
The importance of theoretical suggestion for the development of new alloys is clear from the
historical record. At the end of the 19th century, cast iron was the only important commercial
alloy not already known to western technology at the time of the Romans. When age hardening
of aluminum was discovered accidentally by Wilm, during the years 1903 -1911, it quickly
became an important commercial alloy under the trade name Duralumin.
The strength and hardness of some metal alloys may be enhanced by the formation of extremely
small uniformly dispersed second-phase particles within the original phase matrix in a process
known as precipitation or age hardening. The precipitate particles act as obstacles to dislocation
movement and thereby strengthen the heat-treated alloys. Many aluminum based alloys, copper-

2. tin, certain steels, nickel based super-alloys and titanium alloys can be strengthened by age
hardening processes.
In order for an alloy system to be able to be precipitation-strengthened, there must be a terminal
solid solution that has a decreasing solid solubility as the temperature decreases. The Al-Cu
(Duralumin is an aluminum alloy of 2XXX group) phase diagram shown in Figure 1 shows this
type of decrease along the solvus between the and + regions. Consider a 96wt%Al – 4wt%Cu
alloy which is chosen since there is a large degrease in the solid solubility of solid solution in
decreasing the temperature from 550°C to 75°C.