engineering materials report lab , paraphrase

Memo Report No.IV College of Engineering and Computer Science California State University, Northridge

Experiment #8- Precipitate Hardening In 2024 Aluminum

To: Guido Conzona

From: Fernando Avila

Date: April 1, 2009

Abstract

This experiment is designed to view the dependence of aging time and hardness on temperature. It takes an in depth look at how specifically aluminum 2024’s hardness and aging time vary with temperature. The process of Solution treatment is used to heat treat the samples of aluminum 2024. Through this method it is discovered that with natural aging a higher strength is obtained as opposed to an artificial aging process that involves reheating. This is explained by taking a look at the binary phase diagram of aluminum-copper in the aluminum rich region, and considering the sizes and dispersion of the precipitates formed within the material.

Description of Work

Five samples of 2024 Aluminum were taken and marked for identification purposes. Their initial Hardness values were then recorded using the rockwell B scale. All five specimens were then taken and placed in a furnace for solution treatment at 500 0C for thirty minutes.

One sample was removed from the rest and quenched in water for ten minutes. This sample was chosen to go through a natural aging process. It’s hardness was measured using the Rockwell B scale for time intervals of 3 minutes, 10 minutes, 1 hr, and 2 hours, 1 day, and 1 week.

The remaining four samples were then taken and put through an artificial aging process. First they were removed from the furnace and quenched in water. Once they cooled ten minutes were waited out then their hardness readings were taken using the Rockwell B scale. The samples were then put in another furnace at the temperature of 190 0C. Samples were then removed according to 3 minute, 10 minute, 1 hr, and 2 hr time intervals. After each sample was removed according to it’s specific time interval, they were then quenched in water and their hardness values were measured.

Results and Discussion

Temperature affects the time it takes for a material to age. The higher the temperature used, the less time it takes to age the material and vise versa. This is due to the spacing of the precipitates being dependent on temperature. The higher the temperature initially used the wider apart the precipitates. The hardness of a material is also affected by temperature, the lower the temperature used the higher the hardness reached by the end of the aging period.

After one week the two specimens that were subject to additional heating (190 0C) after the initial solution treatment for time intervals of 3 minutes and 10 minutes, had gone down in hardness. This is due to the much larger aging time. Within a weeks time the samples had a long period of time to come into thermal equilibrium with their surroundings. Once thermodynamic equilibrium was reached the large precipitated within the material grew while the smaller ones shrunk. This in turn lowered the overall energy of the system. The precipitates start moving farther apart and end up lowering the hardness of the material.

If 2024 aluminum were to be used in an application of 190 0C the main problems that will be encountered are loss of hardness with increased aging. This would be an immense problem considering that the process of hardening would be used in order to obtain desired results. The decrease in hardness with time would be a major set back in any application of 2024 aluminum.

The major error in this experiment are the ones made by the ones performing the experiment. It could be possible to eliminate the “human error” from the experiment, but there still exists the possibility that a machine used be miss calibrated. Being either the Furnace thermometers or the rockwell hardness machines. If either one of the machines is not calibrated properly or is not set according to the experiment’s needs the results might not come out as required.

Data

Graph.I

Graph.II

� EMBED MSGraph.Chart.8 \s ���

� EMBED MSGraph.Chart.8 \s ���