The opening of a large mill for aerospace aluminum is a rare event. It is all the more remarkable that the world's newest such factory should open in China, instead of Western Europe or North America, where the industry's decades-old plants are concentrated. But the manufacturing of aircraft structures is increasingly moving to Asia, so one of the biggest suppliers of aerospace-grade aluminum has headed there, too.

U.S.-based aluminum supplier Aleris formally opened its 35,000-ton-per-annum hot rolling mill at Zhenjiang, 220 km (140 mi.) from Shanghai, in April, having begun pilot production there late in 2012. The plant duplicates Aleris's major aerospace-aluminum facility at Koblenz, Germany, with detail improvements based on experience at that facility.

The $350 million Zhenjiang factory appears to be the most upstream aerospace facility that China has been able to lure with the Comac C919 airliner program, a major aim of which has been to drive development of the country's supplier sector. Aleris is a partner on the C919 program, although Johan Petry, vice president of aerospace business, says the opportunity to open a new plant came from the global rise in aircraft manufacturing and that an Asian location was needed to supply Asian customers, not just those in China.

Planned and built in partnership with Chinese aluminum supplier Dingsheng, the plant is now fully owned by Aleris. It is part of a push by Zhenjiang to become an aerospace supplier, particularly for the C919. Also in the city, state missile and space group China Aerospace Science & Industry Corp. is building a composites plant that will supply moveable surfaces and parts of the tail for the forthcoming Chinese airliner.

Mills take raw aluminum from smelters, alloy it with hardeners, cast it into slabs, roll and stretch them into such products as plate or sheet and then heat-treat those products to improve the characteristics of the metal. The industry is highly secretive about the many details in the process that result in strong, fatigue-resistant and highly consistent aluminum needed for aerospace manufacturing. Plant manager Stefan Moldenhauer discussed the technology guardedly with Aviation Week during a visit before the site's formal opening.

The shift of any valuable and closely held technology to China immediately raises the question of whether the secrets can be kept. No Chinese aluminum miller is now recognized as having the quality to supply the international aerospace market. Local production feeds national aeronautics and space manufacturers but even for them local product has been unsatisfactory in at least one instance. Officially, capsules for the Shenzhou manned space program are made of Chinese aluminum, but a metals-industry official here says the program has used imported aluminum.

Aleris has brought much of its technology to Zhenjiang, otherwise the mill could not operate, but deeper know-how behind the plant's design and processes remains in Germany, says Moldenhauer. Even if a rival hired the entire workforce of Aleris Zhenjiang, it could not replicate plant operations, he says, emphasizing the complexity of and interrelationship between details in the process. Perfecting just one part of the process would be a great challenge, and it would not be enough.

Among the technologies that are discussed is one that is well known: the force applied in rolling aluminum plate is crucial to its fatigue resistance. Accordingly, the Zhenjiang mill has been equipped with what Aleris says is the most powerful rolling mill in the global industry, a Siemens VAI unit capable of applying a force of 6 meganewtons (1.35 million lb.) as it squeezes slabs into plates.

The Zhenjiang mill is not yet producing salable aerospace aluminum. It must first prove itself with lower-grade aluminum for other industries and work on reaching the AS9100 certification standard necessary to supply aerospace. That should be achieved after a year of operation. The plant will make 7050, 7075 and 2024 aluminum—conventional aerospace grades, not the more recent types called advanced aluminums, nor the alloys aluminum-lithium and aluminum-magnesium-scandium. Aleris has for years been working intensively on the latter alloy in Germany, and more recently on aluminum-lithium, a favored product of rival Alcoa. The third big supplier to aerospace, Constellium, opened an aluminum-lithium foundry at Issoire, France, in March. Aleris says it will not supply military customers from Zhenjiang.

The advantages of producing in Asia are simply cheaper and quicker deliveries to Asian customers, says Petry. The cost of raw materials is little affected, because the expensive 99.94% pure raw aluminum needed for aerospace alloy is available locally. If the market is big enough, the Zhenjiang plant's whole capacity of 35,000 tons a year can be devoted to aerospace product. Aleris estimates Asian demand for aerospace aluminum at 45,000 tons a year. Japanese producers such as Furukawa-Sky are focused mainly on their domestic market, which they do not fully satisfy; Japanese aerospace manufacturers are major aluminum importers.

Zhenjiang should be producing at its current designed capacity by year-end. The factory building is far from full, because Aleris has provided for expansion. Petry specifically mentions the possibility of a bigger stretcher, an enormous piece of equipment that literally stretches plate from the rolling mill to greater lengths and thinner thicknesses for such purposes as wing skins. The current stretcher at Zhenjiang can pull plates to a length of 24 meters (79 ft.) and is intended for narrowbody aircraft, such as the C919.

Of the more than 300 people who work at the plant, 150 were trained in Germany.

Industry officials say two Chinese aluminum suppliers, Nanning Nannan Aluminum and China Southwest, are working toward achieving production quality that would satisfy international aerospace standards. If and when they do, the global aerospace industry's material supply will again tilt toward China.