Some questions and answers

1. I know what heat treatment and water quenching mean, but what is cold-worked, a rolling ingot, and an artificial ageing treatment?

Cold working is the process of plastically deforming a material at or near room temperature.

An ingot is a large chunk of metal that has been cast,

Artificial ageing is the process of reheating to a moderately low temperature a material that has been solution treated to begin a precipitation reaction, and thereby strengthen the material.

2. 2195 is a newer aluminum alloy, but a significant amount of time has passed since the creation of the alloy and the armored vehicletesting analysis. Once a alloy is created,what kind of material specification testing is conducted to rate the strength of the material? Why weren't the capabilities of the material for use in armor plating known until only recently?

Most alloys are developed in response to a specific need; subsequently, engineers may look at a new material for other applications. Aluminum-lithium alloys were developed specifically for aerospace applications. To be considered for armor plate, someone or some group in the engineering community, military or civilian, had to convince managers to invest time and money in testing the alloy for this purpose. No specific comments on why this did not happen sooner, except that the recent push for lighter weight vehicles probably prompted interest in aluminum alloys.

The process of certification of materials for many applications, includiing aerospace and military use, often requires many years of work and testing. What teting is done depends upon the specific application, but strength testing may involve tensile testing, fatigue testing, creep testing, fracture toughness, and others.

3. Aluminum and copper are two rather soft metals. How do they change properties (such as rigidity) when combined, when individually they are weak?

Alloying changes properties by changing the structure of a material. Simply making a solid solution of copper in aluminum strengthens the aluminum through solution strengthening, in which dislocations have geater difficulty moving through the distorted atom arrangement of the solid solution.

In addition, alloying aluminum with copper results in an alloy that is heat treatable. When solution treated, quenched, and aged, the aluminum alloy becomes significantly stronger.

4. What does ballistic mean?

Websters: pertaining to the motion of a body in flight.

What is artificial ageing?

See answer in question 1.

5. What exactly is the metallographic analysis described in the first paragraph on page 52 of the article on armor plate?

Metallographic analysis is the process of examining and interpreting the microstructure of a material. A specimen is prepared for examination under a microscope by polishing and etching its surface. The image of this surface is examined at, usually, high magnification to determine the feature of its structure.

For example, figure 1 shows how the alloy grains have been elongated by cold rolling the alloy, and that the alloy has not been subsequently heat treated (recrystallized).

6. In T8P4, T means heat treated. What does the P mean?

T8 means solution treat, water quench, and cold work prior to ageing according to a standard procedure; additional numbers and letters specify modifications to the standard procedure.