Need to Know: Heat-Treating Technique...

April 4, 2006
...doubles the strength of HPDC aluminum

Some applications of aluminum high-pressure diecastings (HPDC) have been hampered because available heat-treatments used for wrought and other cast parts cannot be used to increase their strength values. That limitation may be nearing an end.

Australian researchers claim to have developed a novel heat-treating process that can be used with diecastings to increase their strength. "Conventional heat-treatment processes applied to HPDC components cause major blistering and distortion that occurs when air bubbles trapped under pressure during casting expand as they are heated. This ruins the parts," explains Dr. Roger Lumley of the Commonwealth Scientific and Industrial Research Organization (CSIRO). "We have developed a heat-treatment procedure that provides large strength improvements and an excellent surface finish, without blistering or distortion."

Not only is it safe to use the process with diecastings, but trials at CSIRO's laboratories have shown that the new heat-treatment can at least double the strength of high-pressure diecast parts.

Diecast parts can be designed to be lighter than they would be without the new heat-treatment process, and still effectively and safely perform the same task. This would especially appeal to automakers because it would contribute to weight reduction in cars and other vehicles, which in turn would use less fuel.

"A lot of these components are designed for their loads. Basically, the stronger the material, the lighter you can make the part," says Lumley. "We would like to think that we could see a 30% weight reduction compared to current aluminum castings. The diecasting industry is very, very cost sensitive, and if you can use less metal per car part, you also save money," he adds."

"We've done trials on large batches of parts purchased from industry and developed treatments for those parts. That has gone really well. The trials show very few rejects due to heat treatment. In a recent batch of 575 parts, for example, only 1% of the parts were rejected due to blistering."

Lumley says that while aluminum high-pressure diecasting worldwide is dominated by the automotive industry, other industries could put the new technique to use as well, such as builders' nail-gun casings and door handles.

Worldwide, HPDC accounts for approximately 50% of all aluminum castings; however, at the present time, most parts cannot be heat-treated to improve their mechanical properties, because of the blistering problem.

"Basically anything that requires cost-effective mass production of fairly complex high-strength aluminum castings can utilize this process," Lumley says. He believes the new process could halve the cost of producing high-strength parts, which previously could only be made by alternate, more expensive manufacturing processes.

Process particulars are being withheld while international patents are pending. However, CSIRO in conjunction with the Australian Die Casting Association and other Australian companies will have exhibits at the SAE World Congress 2006 and the Metalcasting Congress as well as lectures at the International Conference on Aluminum Alloys and at the Australian Die Casting Association conference this year.