Create "7050" for C919! Documentary Materials on Independent Development of Aluminum Materials for Domestic Large Aircraft | Aluminum | Domestic

On May 28th, the domestically produced large aircraft C919, which took off from Shanghai, landed smoothly at the Capital Airport, marking the first successful commercial flight with passengers.

At that moment, Southwest Aluminum Industry Co., Ltd. of China Aluminum Group, located far away in Chongqing, was in celebration - over 50% of the aluminum materials used in C919 came from this enterprise.

Since the establishment of the C919 project, Southwest Aluminum has undertaken the research and production task of domestically produced aluminum materials for large aircraft. Through independent innovation, they have overcome the difficulty of "from scratch" and continuously improved the independent guarantee rate of domestic civil aircraft aluminum materials.

Targeting third-generation advanced aluminum alloys from scratch

In the history of world aviation development, there is a saying that "one generation of aircraft, one generation of materials".

Large passenger aircraft are considered the "jewel on the crown of modern industry", and material performance is the primary factor determining aircraft performance. To manufacture domestically produced large aircraft, it is necessary to achieve material autonomy and control.

Aluminum alloy materials account for 65% of the main materials used in manufacturing commercial aircraft. The most important international third-generation advanced aluminum alloy, 7050 aluminum alloy thick plate, is known as "one of the most difficult aluminum alloys to cast in the industry". Previously, China could not independently produce it.

"'7050 'is widely used in the manufacturing of key load-bearing components such as aircraft wing beams, ribs, fuselage frames, and wall panels, and is an indispensable key material. Zhou Hua, Deputy Chief Engineer and Project Leader of Southwest Aluminum Technology Center, told Science and Technology Daily reporters that the key production technology of 7050 aluminum alloy thick plates has always been regarded as a core technology secret by developed countries, and is strictly blocked.' Imported materials not only have prices as high as tens of thousands of yuan per ton, but are also often restricted from foreign purchases. '"

"Without any experience to learn from, we started completely from scratch." Yang Rongdong, the director of Southwest Aluminum Technology Center with gray hair, recalled his time with great enthusiasm.

In 2005, Southwest Aluminum formed a joint research and development team with some universities and colleges; At the same time, professional technical personnel in the fields of casting, rolling, forging, and testing are also selected within the enterprise to form a project team. They started systematic research on industrial preparation technology from the preparation of large-sized 7050 aluminum alloy ingots, thick plate rolling, heat treatment, and other aspects.

"At that time, everyone was holding back their determination to develop the third-generation advanced aviation aluminum alloy!" Yang Rongdong said.

Breaking the "curse" of ingot cracking after a hundred failures

7050 aluminum alloy thick plate has high strength, toughness, fatigue resistance, and damage resistance, which is an unprecedented test for the purity of raw materials and casting technology. At that time, the equipment and tooling of the Southwest Aluminum melting and casting plant were relatively backward, and the formation of the 7050 large-sized ingots was the first obstacle encountered by the team.

"New materials require high strength, and the first challenge during casting is that they are prone to cracking," said the supervising engineer Chen Xinmin. During that time, project team members were stationed at the furnace for 24 hours from the beginning of casting, waiting for the final shape to be formed after smelting.

In general, minor cracking does not affect the use of aluminum alloys, but it is not suitable for civil aviation materials. The latter has higher safety requirements, not only requiring airworthiness certification, but all types of materials must meet various standards and have a service life of about 15 years.

"At that time, I was most afraid of hearing a 'bang' sound, which was that the ingot had cracked." Zhou Hua said that at first, there was no pilot production line, and all the tests were directly completed on the enterprise's production line. A batch of raw materials was worth four to five hundred thousand yuan, and cracking meant that all were scrapped.

During that period, ingot cracking occurred frequently, with the melting and casting plant stacking thousands of tons of cracked ingots, resulting in losses of tens of millions of yuan. Everyone was both distressed and anxious, suppressing their anxiety while groping to adjust parameters. The project team members have been living and eating in the office for several months. According to job responsibilities, some continuously calculate and adjust the concentration ratio of alloys, while others improve the temperature and cooling methods of the furnace

"At that time, I didn't feel tired at all and only thought about how to overcome this difficult problem," Zhou Hua said.

After hundreds of failures, the project team finally broke the curse of ingot cracking through continuous optimization of alloy composition and proportion. The first formed ingot was born in December 2005.

From "Following" to "Combining" Civil Aircraft Aluminum Materials Going Abroad

The problem of ingot forming has been solved, and another major challenge has arisen before the project team.

In 2008, the project advanced in depth and successively produced qualified 60mm and 80mm thick plates. However, during the trial production of 100mm, 120mm, and 150mm thick ultra thick plates, the fatigue performance and high tensile performance of the products frequently failed to meet the standards. Project research is like stepping into a "black hole".

"After repeated comprehensive dissection and analysis of the samples, the project team innovatively proposed new insights into the relationship between material structure and properties," said Wang Zheng'an, Chief Engineer and then Deputy Director of the Technical Quality Department.

Afterwards, the project team went through multiple failed verifications in terms of billet specifications, rolling processes, and parameter control, and finally formed a mature process plan in 2009, producing qualified ultra-thick plates.

In 2015, Southwest Aluminum developed the largest cross section 7050 aluminum alloy ultra wide and ultra thick pre stretched plate in China after breaking through a series of key technologies such as large-scale ingot preparation, strong deformation rolling, strong toughness heat treatment, and residual stress control. A complete industrial manufacturing technology system for 7050 aluminum alloy pre stretched plates was established, achieving industrial production of full thickness products ranging from 6.0mm to 203mm, and achieving large-scale application in multiple key models of equipment in China's aerospace industry.

Since 2017, China Aluminum Group and COMAC have jointly identified 21 key main structural aluminum materials and collaborated with domestic advantageous teams to carry out systematic research and development; Southwest Aluminum has become the first qualified supplier of domestically produced aluminum materials for large aircraft in China. As of now, it has provided over 600 pieces of aluminum alloy materials in 30 specifications for C919.

In addition to supporting the domestic aviation market, Southwest Aluminum's civil aircraft aluminum materials have already gone abroad. On May 23rd, China Aluminum Southwest Aluminum, Boeing, and AVIC International signed a forging project agreement in Chongqing to provide forgings for the Boeing 787 aircraft model.

"Compared with internationally advanced aluminum material enterprises, we used to be 'running with', but now we have reached the stage of 'running with', striving to become a 'leader' in the industry in the future. Li Yong, Secretary of the Party Committee and Chairman of Southwest Aluminum, said, 'The 20th National Congress of the Communist Party of China proposed to accelerate the construction of a strong manufacturing and aerospace country. Southwest Aluminum will resolutely fulfill its mission as a' leader, main force, and leader ', and play a' pillar 'role in serving national strategies!'"