Plot the hardness vs time of aging for each aging temperatur

Plot the hardness vs. time of aging for each aging temperature, using Excel. How does aging temperature affect the time and hardness? What happens to the 190 degree C (370 degree F) 3 and 10 minute specimens after one week? Why? If you were going to use 2024 AI in an application at a temperature of 190 degree C (370 degree F), what problems could be encountered? Discuss errors in this experiment and their sources.

Solution

3. Aging or precipitation hardening temperature affect the time and hardness to a great extent. Usually, hardness of metals decreses with increase in temperature. However, the time taken by specific to loose its hardness depends on the temperature to which it is exposed. For example, if a metal specimen is exposed to 100 degree Celcius would take more time to loose its hardness than if it is exposed to 250 degree Celcius. It must be noted that, when specimen is exposed to the elevated temperatures its hardness first increases due to its internal thermal resistance but over time heat overcomes its internal thermal resistance thereby reducing its hardness linearly with increase in temperature.

4. After one week the specimen heated for 3 minutes would be have attracted more corrosion as compared to the specimen heated for 10 minutes. The reason for this is that when specimen is exposed to the elevated temperatures for significant amount of time its internal structural morphology is changed and hence after treatment there are hardly any valence atoms are left in the outer molecular orbit to form bond with oxides and corrode the material.