Metal and Technology, Inc. We support the realization of social ecology through the utilization of technology that uniformly disperses carbon in non-ferrous metals.

Carbon-added aluminum copper alloys

1. Development Background

Background to the development of carbon-added aluminum-copper alloys

Against the backdrop of environmental changes such as global warming in recent years, there have been urgent calls for the development of new structural materials that contribute to weight reductions in automobiles and train carriages in order to meet societal demands for energy savings, lower cost, and reduced CO2 emissions.
Although the addition of carbon to non-ferrous metals by conventional methods has been difficult, we succeeded in adding carbon to lead-free solder alloy and pure copper to increase their mechanical strength. This work was done in collaboration with Professor Emeritus Kenichi Ohshima of the University of Tsukuba and our partner company Shirogane, and we have obtained patents for this technology.
In recent work, we successfully expanded this technology to structural refinement of aluminum copper alloys by adding and evenly dispersing carbon particles in the alloy. This is excepted to result in increased mechanical strength.
Our company is currently making a joint application together with Shirogane for a patent related to carbon-added aluminum copper alloys.

Company president Ito with Professor Emiritus Ohshima of the University of Tsukuba (also a board member of our company) on the university's campus
<Company president Ito with Professor Emiritus Ohshima of the University of Tsukuba
(also a board member of our company) on the university's campus>

2. Characteristics and Structure

Characteristics of carbon-added aluminum copper alloys

Anticipated improvements in mechanical strength and extensibility.
The addition of carbon to aluminum copper alloys is expected to improve their mechanical strength and extensibility, similar to how the addition of carbon to iron leads to improved properties in carbon steel. Also, carbon addition will improve corrosion resistance. Tensile strength measurements using a universal testing machine found that the tensile strength of the carbon-added alloy was more than twice that of the alloy without carbon, making the strength comparable with that of duralumin A2017, a representative aluminum alloy (*see supplemental material). These results demonstrate that the strength of pure alloys can be greatly increased by carbon addition. The increased strength of the carbon-added alloy is attributed to structural refinement, with the refined structure providing resistance when a load is applied.

Structure and strength of carbon-added Al-5 wt.%Cu alloy

Scanning electron microscopy (SEM) observation of the surface structures of carbon-added Al-5 wt.%Cu and carbon-added Al-5 wt. %Cu-0.3 wt. %C alloys showed that the aluminum copper alloys developed by our company have a refined structure due to carbon addition (Fig. 1).
Therefore, to investigate how carbon affects the structural refinement, we performed elemental analysis using an X-ray microanalyzer (XMA) to produce a color map of each element and determine the distribution of carbon in the Al-5 wt. %Cu-0.3 wt. %C alloy. As a result, we observed that carbon was evenly distributed throughout the entire structure (Fig. 2(c)). It was inferred that the added carbon impeded growth of the alloy structure, leading to the structural refinement.

Figure 1: Comparison of alloy surface structures

Compared with the carbon-free alloy, the carbon-added aluminum copper alloy had a more refined structure and increased areas of gray, which indicates alloying between aluminum and copper.

(a) AlCu5%(carbon-free)
(a) AlCu5%(carbon-free)
(b)AlCu5% C 0.3wt%
(b)AlCu5% C 0.3wt%

Figure 2: Color mapping image of Al-5 wt. %Cu-0.3 wt. %C observed by electron probe microanalyzer (EPMA)

Carbon is evenly dispersed through both the aluminum phase and the aluminum copper alloy phase. It was inferred that carbon addition impeded growth of these phases, refined the structure of the aluminum copper alloy, and increased its strength.

Anticipated reduction in manufacturing costs due to simple composition.
Anticipated reduction in manufacturing costs due to simple composition. Almost all aluminum alloys used in actual materials such as duralumin (A2017) and AC2A contain copper, but they also contain other non-ferrous metals such as magnesium and manganese, which make manufacturing difficult and increases the costs due to the complex composition. In contrast, carbon-added aluminum alloys are expected to have mechanical strength equivalent to or better than that of existing products despite having a simpler composition consisting of just aluminum, copper, and carbon.

3. Future Prospects

Future research and development

Addition of carbon to existing aluminum alloys such as AC2A
Our carbon addition technology has been successfully applied to the aluminum alloy AC2A, which is used in things such as engine parts for automobiles. The alloy's strength is improved by the addition of carbon. We are currently conducting research and development to further advance this technology by focusing on the optimal combination of added carbon amount and heat-treatment parameters for the widely used AC2A, with the goal of developing aluminum alloys that have low cost, high reliability, and high strength.
This research and development was nominated for the 2015 Strategic Foundation Technology Advancement Support Project (Sapoin Project) conducted by the Small and Medium Enterprise Agency of the Ministry of Economy, Trade and Industry, Japan, and we are planning to develop and commercialize carbon-added AC2A in around two years' time.

Anticipated range of use

We aim to utilize the high strength and high extensibility of carbon-added aluminum copper alloys to contribute to weight reductions by using it as a substitute for the aluminum alloys that are used in automotive structural materials and engine parts.
Furthermore, we are also aiming for our carbon-added aluminum copper alloys to be utilized as a material for improving strength in a wide variety of non-automotive applications of aluminum alloy, for example, in aluminum sashes, aluminum boxes, and transport equipment such as ships and train carriages.

Supplemental material

This heat-treatable aluminum alloy known as duralumin has excellent cutting workability and strength.
Aluminum alloys that contain copper (Cu) tend to have high strength and low workability (plastic working).
Although the strength of duralumin is on par with iron and steel materials depending on the environment, duralumin tends to have poor weldability and corrosion resistance compared to other aluminum alloys. It is used in airplanes, hydraulic equipment, and other applications.

Composition of A2017 (aluminum)
Alloy number Si Fe Cu Mn Mg Cr Zn Ga,V,
Zr etc.
Ti Other Al
Individual Total
A2017 0.20 to 0.8 0.7 or less 3.5 to 4.5 0.40 to 1.0 0.40 to 0.8 0.10 or less 0.25 or less - 0.15 or less 0.05 or less 0.15 or less Remainder

AC2A is a cast aluminum alloy based on Cu and Si that is known for its good casting properties.
Since it contains copper, it has somewhat worse corrosion resistance than materials that do not. This material is called wrought aluminum, and it has excellent tensile strength.
AC2A is a general-use material that has applications including manifolds, differential carriers, pump bodies, cylinder heads, valve bodies, and crank cases.

Composition and elements in AC2A (cast aluminum material)
Alloy number Cu Si Mg Zn Fe Mn Ni Ti Pb Sn Cr Al
AC2A 3.0 to 4.5 4.0 to 6.0 0.25 or less 0.55 or less 0.8 or less 0.55 or less 0.30 or less 0.20 or less 0.15 or less 0.05 or less 0.15 or less Remainder