China Material Sciences

I'm going to put all the interesting articles regards to advancements of materials sciences in China on this thread. I'll start with this article on Friction Stir Welding.



Friction stir welding of aluminium ships

Fred Delany, Stephan W Kallee, Mike J Russell

TWI China, Baliqiaobei Chaoyang District, P O Box 863, 100024 Beijing, P.R. China
Tel: +86 (0)10 8570 3255, [email protected]

(excerpts)

Paper presented at 2007 International Forum on Welding Technologies in the Shipping Industry (IFWT) Held in conjunction with the Beijing Essen Welding and Cutting Fair in Shanghai, 16-19 June 2007

In friction stir welding (FSW), which has been invented and patented by TWI (References [1] and [2] ), a wear resistant rotating tool is used to join sheet and plate materials such as aluminium, magnesium and copper. In laboratory experiments, zinc, lead, titanium, nickel and steel have been friction stir welded. The welds are made below the melting point in the solid phase. The excellent mechanical properties and low distortion produced by FSW are attributed to the low heat input and smooth profile of the weld.

The relatively low temperatures generated during friction stir welding permit joining of thin aluminium skins of honeycomb or sandwich panels, avoiding delamination of skins and core. Low temperature FSW also permits a number of dissimilar material welds to be made.

Since the invention of friction stir welding at TWI in 1991, companies from all parts of the world have implemented the process, predominantly in the fabrication of aluminium components and panels. Trendsetters were the Scandinavian aluminium extruders, who were in 1995 the first to apply the process commercially for the manufacture of hollow aluminium deep-freeze panels, and for ship decks and bulkheads. Friction stir welded structures are now revolutionising the way in which high-speed ferries, hovercraft and cruise ships are built from prefabricated lightweight modules ( Fig 1&2).

In the shipbuilding industry several companies use the FSW process for the production of large aluminium panels, which are made from aluminium extrusions. Commercial FSW machines are now available and include complete installations to weld up to 16m lengths. Currently 171 organisations hold non-exclusive licences from TWI to use the process. Most of these licensees are industrial companies, who exploit the FSW process in commercial production in Japan, USA, China, Europe and Scandinavia."


"Batch production by FSW also reduces the welding workload in shipyards. Shipbuilding changes from manual fieldwork to standardised production lines. Production efficiency of shipbuilding is therefore greatly improved. And finally, the residual stresses of friction stir welded aluminium alloy panels are very low and distortion is very small. Parts of ships can therefore be assembled more accurately, and the precision of ship modules and the final shape of ships can be significantly improved. Nowadays, the concept of using prefabricated FSW panels for shipbuilding is popular at shipyards in Dalian, Shanghai, Wuhan, Guangxi and Guangzhou. These wide panels have successfully been used in many shipbuilding projects, including ships designed and fabricated in China for export to Vietnam and Micronesia ( Fig.25).
FSW used on Chinese aluminium alloy ships for various export markets Fig.25. FSW used on Chinese aluminium alloy ships for various export markets

The Type 022 Houbei Class is the Chinese People's Liberation Army Navy's new-generation stealth missile fast attack craft (FAC). The boat features a unique high-speed, wave-piercing catamaran hull with evident radar cross-section reduction design features ( Fig.26). A number of Chinese shipyards across the country have been involved in the construction of the boat and it has been reported that FSW aluminium alloy panels have been used to produce this very advanced navy vessel in China."

I find this paper interesting because not only it mentions FSW, but doing it on AL-Li. Aluminum Lithium is a new cutting edge alloy that is the aluminum industry's answer to composite technologies. If composite advocates talk about being more durable, lighter and stronger than Aluminum, Aluminum Lithium alloys is the counter.



Author : Acta Metallrugica Sinica
Published: May 11, 2004

Friction stir welding (FSW) for 5 mm thick Al-Li alloy rolled sheet material has been completed with a cone-shape screw thread pin. The metallurgy experiment demonstrates that the dynamic recrystallization occurs in the weld nugget zone (WNZ), fine equiaxed grains form, and a large number of segregation phases appears at grain boundaries. The microstructure in the heataffected zone (HAZ) consists of coarse bar-shape recovery grain, and that of the thermo-mechanically affected zone (TMAZ) exhibits bent band-like character, but the deformation degree at the advancing side is bigger than that at the retreating side. Microstructures in TMAZ are also recovered, and the amount of recovery grain at retreating side is more than that at advancing side. Tensile test shows that the joint strength and elongation are 345 MPa at welding rate v=40 mm/min, and 9.6% at v=60mm/min respectively. Hardness measurement shows that the FSW joint is soften during welding, and the softened zone at advancing side is wider than that at retreating side. Fractographs confirm that the fracture of the joint is mixed mode of ductile and brittle fracture.

The use of FSW for lightweight aircraft structures. This suggests to me China is much more interested in building aircraft rather than increasing composite content, to use AL and AL-Li alloys via processes like FSW.

I find papers like these far more interesting in terms of pointing to where China's future generation of fighters would head into, rather than pics of F-22 like models in air tunnels and fan based drawing and dreams of stealth fighters.

If you still don't know what carbon nanotube technologies are and what hold for in the future, its time that you should. CNT (namo jushi) is considered one of the four branches China considers strategic for its future.



Microwave Absorption of Single-Walled Carbon Nanotubes/Soluble Cross-Linked
Polyurethane Composites
Zunfeng Liu,† Gang Bai,† Yi Huang,† Feifei Li,‡ Yanfeng Ma,† Tianying Guo,† Xiaobo He,§
Xiao Lin,§ Hongjun Gao,§ and Yongsheng Chen*,†
Key Laboratory of Functional Polymer Materials and Center for Nanoscale Science and Technology,
Institute of Polymer Chemistry, The College of Chemistry, Nankai UniVersity, The College of Physics,
Nankai UniVersity, Tianjin 300071, China, and The Institute of Physics, Chinese Academy of Sciences,
eijing 100080, China
ReceiVed: April 24, 2007; In Final Form: June 29, 2007
Processable composites of single-walled carbon nanotubes (SWNTs) with soluble cross-linked polyurethane
(SCPU) were prepared at various loadings of SWNTs (0-25 wt %), and they exhibited strong microwave
absorption in the microwave range of 2-18 GHz. For example, 5 wt % loading SWNTs/SCPU composite
has a strong absorbing peak at 8.8 GHz and achieves a maximum absorbing value of 22 dB. The absorbing
peak position moves to lower frequencies with increasing SWNT loading. Theoretical simulation for the
microwave absorption using the transmission line theory agrees well with the experimental results.
The microwave absorption of these composites can be mainly attributed to the dielectric loss rather than
magnetic loss.

Another piece of FSW with AL-Li work.



Microstructures and Mechanical Properties of Al-Li Alloy Friction Stir Welds with a Cylinder-shape
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words : 300
Article Summary by: TsingHua
Author : Journal of Materials Engineering
Published: March 25, 2004
This abstract was translated from 柱形光头搅拌针搅拌摩擦焊接铝锂合金接头组织及力学性能
Friction stir welded 5 mm thick, Al-Li alloy rolled sheet, metallurgical, hardness and tensile strength measurements were performed. The results demonstrate that there exist three distinct zones in the FSW joint: the weld nugget zone (WNZ), and the thermal-mechanically affected zone (TMAZ), and the heat-affected zone (HAZ). The microstructures in WNZ take on scale shape. Under the thermal cycle, the microstructures in HAZ occur recovery and generate the bar-shape recovery structure. The microstructures in TMAZ consist of the equiaxed grains, and the grain size of the microstructures at the retreating side is bigger than that at the advancing side. The tensile test results confirm that the highest tensile strength of Al-Li FSW joints welded with a cylinder-shape and non-thread pin is 296MPa(under the welding speed υ =40mm/min), and the highest elongation percentage is 8.6%( under the welding speed υ =80mm/min).The hardness measurements show that the weld is softened, and the softened scope of both the advancing and the retreating sides are almost the same. But the soften degree of the material at the retreating side is higher than that at the retreating side.

Some guys playing around with aircraft grade aluminum alloy.



Friction stir welding of 2219-O aluminum alloy
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Article Abstract by: TsingHua
Author : Transactions of the China Welding Institution
Published: January 25, 2006
This abstract was translated from 2219-O铝合金的搅拌摩擦焊接
2219-O aluminum alloy was friction stir welded to investigate the effect of friction stir welding on its microstructure and mechanical properties in this paper.The microstructures of different zones in the joint were analyzed by optical microscopy,and the mechanical properties of the joint were evaluated by means of tensile tests.Microstructural analyses indicated that the weld nugget zone(WNZ) is composed of fine isometric grains because of continuously dynamic recrystallization,and more precipitates formed in this zone.In the thermal mechanical affected zone(TMAZ),the grains have experienced incomplete recrystallization due to seriously plastic deformation,and some small grains begin to nucleate.In the heat affected zone(HAZ),all the grains are coarsened.Tensile tests showed that the tensile strength of the joint is the same as that of the base metal,and the fracture occurs in the base metal when the tool rotation speed was 800rpm and the Welding speed was less than(400mm/min.) On the other hand,when the welding speed was greater than(400mm/min,) the mechanical properties of the joint significantly degrade and the joint fractures at the defect location because of the formation of a defect in the WNZ.

Local boy makes good.



May 14, 2008

Even before Weixiao Huang received his doctorate from Rensselaer Polytechnic Institute, his new transistor captured the attention of some of the biggest American and Japanese automobile companies. The 2008 graduate’s invention could replace one of the most common pieces of technology in the world—the silicon transistor for high-power and high-temperature electronics.

Huang, who comes from humble roots as the son of farmers in rural China, has invented a new transistor that uses a compound material known as gallium nitride (GaN), which has remarkable material properties. The new GaN transistor could reduce the power consumption and improve the efficiency of power electronics systems in everything from motor drives and hybrid vehicles to house appliances and defense equipment.

“Silicon has been the workhorse in the semiconductor industry for last two decades,” Huang says. “But as power electronics get more sophisticated and require higher performing transistors, engineers have been seeking an alternative like gallium nitride-based transistors that can perform better than silicon and in extreme conditions.”

Each household likely contains dozens of silicon-based electronics. An important component of each of those electronics is usually a silicon-based transistor know as a silicon metal/oxide semiconductor field-effect transistor (silicon MOSFET). To convert the electric energy to other forms as required, the transistor acts as a switch, allowing or disallowing the flow of current through the device.

Huang first developed a new process that demonstrates an excellent GaN MOS (metal/oxide/GaN) interface. Engineers have known that GaN and other gallium-based materials have some extremely good electrical properties, much better than silicon. However, no useful GaN MOS transistor has been developed. Huang’s innovation, the first GaN MOSFET of its kind in the world, has already shown world-record performance according to Huang. In addition, Huang has shown that his innovation can integrate several important electronic functions onto one chip like never before. “This will significantly simplify entire electronic systems,” Huang says. Huang has also designed and experimentally demonstrated several new novel high-voltage MOS-gated FETs which have shown superior performance compared to silicon MOSFET in terms of lower power consumption, smaller chip size, and higher power density.

The new transistors can greatly reduce energy loss, making energy conversion more efficient. “If these new GaN transistors replaced many existing silicon MOSFETs in power electronics systems, there would be global reduction in fossil fuel consumption and pollution,” Huang says.

The new GaN transistors can also allow the electronics system to operate in extremely hot, harsh, and high-power environments and even those that produce radiation. “Because it is so resilient, the device could open up the field of electronic engineering in ways that were not previously possible due to the limitations imposed by less tolerant silicon transistors,” he says.

Huang has published more than 15 papers during his time as doctoral student in the Dept. of Electrical, Computer, and Systems Engineering at Rensselaer. Despite obvious difficulties, his parents worked tirelessly to give Huang the best possible educational opportunities according to Huang. And when school wasn’t enough, Huang’s father woke him up early every morning to practice mathematical calculations without a calculator, instilling in Huang a lifelong appreciation for basic, theoretical mathematics and sciences.

He received a bachelor’s in electronics from Peking Univ. in Beijing in 2001 and a master’s in physics from Rensselaer in 2003. He will receive his doctorate from Rensselaer on May 17, 2008 and plans to work as a device engineer in the semiconductor industry.

SOURCE: Rensselaer Polytechnic Univ.

The use of carbon fiber epoxy on the Chinese defense military industry. Also covers the subject matter of electronics. Interesting to note the rudder of the Q-5 is composite.



Excerpts.

"Hexcel, the third co-owner of BHA, is a Connecticut-based company that
produces advanced structural materials,64 including carbon fibers that are used in the U.S.
F18, F22, and F35 fighter planes.65 In 2006, Hexcel agreed to pay $203,400 to settle
charges that it committed 22 violations of Commerce Department export control
regulations,66 including three charges of illegally exporting AS4C carbon fabric to China
in 2002,67 the same year that BHA formally opened.68 Under the VEU system, Hexcel
now will be able to ship this product (ECCN 1C010.b) to BHA without applying for an
export license.69 Hexcel also agreed in 2007 to pay $15 million to settle allegations that
it knowingly used defective fiber in bulletproof vests sold to U.S. law enforcement
officers.70 Hexcel’s record does not inspire confidence in its willingness to abide by
government regulations."

"AVIC I has a number of military subsidiaries that could benefit from the items
eligible for license-free export to BHA (see Annex II). Chengdu Aircraft Industry
(Group) Corporation, Ltd. (CAC)71 builds the J-10 (F-10), a fourth generation Chinese
fighter first deployed late last year.72 CAC is equipped with a composite materialmachining center,73 and could use carbon fibers (1C010.b)74 or resin-impregnated fibers
(1C010.e)75 diverted from BHA to produce composite parts for the J-10, which would
improve the aircraft’s performance. Another AVIC I subsidiary, Xi’an Aircraft Industry
(Group) Company, Ltd. (XAC),76 developed and manufactured China’s nuclear-capable
B-6 (Hong-6) bomber.77 This bomber has been improved with features such as new
engines for extended range78 and an aerial re-fueling capability,79 and is reportedly being
adapted to carry cruise missiles.80 Composite materials from BHA could be incorporated
into these improved versions, giving AVIC I’s B-6 greater range and better performance.
A third AVIC I subsidiary is China Aircraft Strength Research Institute,81 which could
benefit from the diversion of non-destructive inspection equipment for use with
composites (1B001.f).82 This subsidiary has conducted full-scale verification tests forfighters and bombers83 and studies the strength and damage resistance of composite
materials.84 The Institute has helped develop a composite vertical stabilizer for China’s
Q-5 fighter.85
In addition to these three AVIC I subsidiaries, there are several other subordinates
that could benefit from a diversion of some or all of the items now eligible for licensefree
export to BHA. Other AVIC I subordinates include the National Defense Key
Laboratory for Advanced Composites, a research center under AVIC I’s Beijing Institute
of Aeronautical Materials86 that focuses on composite materials for missiles.87 Its
scientists published a study on AS4 carbon fiber in 2003,88 the year after Hexcel
allegedly made three illegal shipments of AS4C to China.89 AVIC I also oversees Jinan
Research Institute for Special Aeronautical Composites,90 which designs, tests, and
produces composite materials for military aircraft, missiles, and radar installations,91 andLuoyang Optoelectro Technology Development Center,92 which produces air-to-air and
surface-to-air missiles and air defense systems.93"