Seiji Sasabe

Study on the factors in creating the IMC-free region: dissimilar metal joining of aluminium alloys to steel by a MIG-braze welding by using the advanced hot-dip aluminized steel sheet

Dissimilar metal joining of aluminium alloys to steel is generally difficult to be in practical use because of a formation of brittle intermetallic Fe–Al compound (IMC) at the interface of the joint. The authors have been researching in order to minimize the thickness of this brittle IMC in order to get excellent joint strength and have found that the formation of this brittle IMC is regionally prevented by using the advanced hot-dip aluminized steel sheet and by adopting suitable joining conditions. In particular, this paper focuses on the mechanism of creating this IMC-free region in the case of MIG-braze welding and the results obtained are as follows. (1) The creation of IMC-free region is initiated as the first process by the dissolution of the τ5 phase (Fe–Al–Si) in the aluminized layer into the weld metal, and temperatures of more than 886 K for dissolution during MIG-braze welding and the use of filler metal for dilution of Fe and Si in τ5 phase have significant effects. (2) In the second process, the diffusion between aluminium-alloy weld metal and base steel is restricted by AlN on the surface thin layer of the base steel which existed under 908 K temperature conditions during MIG-braze welding.

Mechanical properties of A6082 welded joints with Nd–YAG laser

Weldability of A6082 with Nd–YAG laser was investigated to explain the advantages over the conventional MIG process. It is concluded that rapid cooling rate in heat-affected zone (HAZ) contributes to increasing joint strength and improvement durability against liquation cracking in HAZ during Nd–YAG laser welding. This is why rapid cooling rate is enough to prevent crossing the C-curve for precipitation of β′ and small volume of weld metal is enough to reduce shrinkage strain during solidification. And the joint strength increased with an increase of manganese content in the base metal, but by contraries the minimum hardness in HAZ where the fracture occurred in the tensile test decreased. This may be attributed to the prevention of intercrystalline embrittlement due to the addition of manganese in case of Al–Mg–Si series alloys with excessive Si content.

Laser welding characteristics of aluminium alloys for automotive applications

Ratification of the Kyoto Protocol, an internationally agreed set of measures intended to prevent global warming, has been approved in Japan where CO 2 emissions in 1999 were up by approximately 9% on the 1990 level (equivalent to around 100 mn tonnes). In this context, various preventive measures haven been proposed to meet the target of a 6% reduction in greenhouse gas emissions by 2010 (in relation to 1990). In transport, the CO 2 emission rate amounts to around 22%. This rate has important implications for efforts to improve the fuel efficiency of motor vehicles, which centres around weight reduction in addition to reduction of running resistance and the development of higher-efficiency engines. With regard to the effect of weight reduction through steel to aluminium material substitution, the energy required for melting and recycling of aluminium scrap amounts to just 3.3% of that consumed during new base metal production (around 2.2% of the CO 2 emission rate after conversion), thus offering huge scope for a substantial reduction in gas emissions per unit source through recovery and recycling of waste aluminium products alone. Based on the prediction of extensive aluminium alloy applications to car bonnets, boot lids, and underbody components in addition to current applications in the manufacture of heat exchangers, wheels, and engines now being widely aluminised, CO 2 emissions can be altogether reduced by some 33.4 mn tonnes/year through fuel efficiency improvements and raw material production, making a 0.3% contribution to efforts to reduce greenhouse gas emissions in relation to the 1990 levels.

Laser braze welding for dissimilar metal joining of aluminium alloys to steel

An important feature of efforts to prevent global warming is the appropriate use of aluminium to reduce the weight of motor vehicles, etc., and this necessitates the development of techniques for joining dissimilar metals to steel. When the combination is steel and aluminium, however, conventional welding techniques bring about the production of brittle intermetallic compounds resulting in weak joints and, currently, onlymechanical joining technologies and the use of adhesives offer a reliable solution. In this study, we develop a welding method using conventional welding equipment (for MIG, laser, and resistance spot welding), in which by using either (1) hotdip aluminized steel sheet or (2) galvanized (GA) steel sheet and optimizing joining conditions, it is possible to achieve dissimilar metal welded joints of aluminium alloy and steel with a strength equivalent to that of aluminium alloy to aluminium alloy welded joints. In this article, we describe the results of the examination of laser braze welding, one of these welding techniques, which involves the use of a laser, a high energy density heat source which is capable of rapid heating and solidification.

Weld cracking and joint strength of 2219 by MIG welding

Weldability of Al–Cu series alloy 2219 with MIG process was investigated in comparison with that of Al–Cu-Mg series alloy 2024. On weld cracking sensitivity, 2219 is superior to 2024 and as for the combination with filler metal, the decrease in Mg content in weld metal causes crack resistance to increase. And a liquation cracking in heat-affected zone was easily initiated in the case of Mg contents more than 1.6 mass% and Cu/Mg (ratio in mass%) less than 1.8 in weld metal. Welded joints were mostly fractured in weld metal even with reinforcement during tensile testing, so the intensification of weld metal is directly connected to the improvement in joint strength and fractured mode. The results of the investigation of correlation between the strength and chemical composition in weld metal revealed that the joint strength increased with an increase in magnesium and manganese but encouraged the weld cracking simultaneously. However, the author has also found that silicon was available for decreasing weld crack and the possibility of consistency with joint strength and crack resistance by control of these contents of Mg, Mn, and Si.

Welding of 2000 series aluminium alloy materials

Duralumin was prepared by Alfred Wilm by using Al–Cu alloys. Dürener Metallwerke Aktien Gesellschaft was established in 1901 at Duren, near Berlin, and it was there that Alfred Wilm developed a new aluminium alloy for use in cartridges in place of brass. Since he had some experience with quench hardening of steel, his research pursued the possibility that aluminium alloys would show the same kind of quench-hardening phenomenon as steel and he discovered that addition of copper and magnesium would result in a tough alloy. A 3mmt Al-4%Cu-1.5%Mg sheet was produced, heated to 5208C in a salt bath, and then quenched in water. Wilm’s intention was to measure the Brinell’s hardness but, having an appointment on Saturday afternoon, he made only rudimentary measurements then and made more comprehensive measurements on the following Monday. The values obtained were surprisingly high and subsequent study revealed the phenomenon known as age hardening. The compound, eventually named Duralumin (2017) after the town, marked its centenary in September 2006. Other well-known alloys are 2024 Superduralumin and 7075 (Al–Zn–Mg–Cu) Superduralumin. All duralumin alloys belong to the highest class of hardness for aluminium alloys.

Laser fusion welding technology of aluminium alloys

This article deals with recent trends in fusion welding of aluminium dividing the techniques into arc welding and laser welding and hybrid welding combining these. As there have been many reports on welding techniques of welding steel and other metals, it also deals briefly with MIG brazing and laser brazing.

Welded joint strength of thin aluminium structures

What are typical applications of aluminium alloy thin structures? They are mostly the ones which require light weight such as machines and appliances for transport, i.e., body frames for airplanes and railway carriages. Since about ten years ago, however, thin aluminium structures have also been used for body frames of cars although the history of this application is not so long as those of the above-mentioned. Aluminium alloys have conventionally been used for engines and some fringe components to reduce weight. The reason behind this new area of application is that a reduction in fuel cost has become vital to meet environmental requirements, in particular, for controlling Co2 gas emission as stipulated for the European automobile industry. The joining methods of these structures will be described briefly below. Aluminium alloys are inferior in weldability to the general range of steels. For airplanes, a commonly used method is mechanical joining using rivets, screws and so on. In body frames of railway carriages, resistance spot welding was first applied, but the arc welding method has later been used since the development of a material (6N01 extrusion moulded material) which has a balanced combination of extrusion mouldability, strength and weldability. How about the joining methods for automobile body frames? Traditionally, car body frames have been made of steels employing the resistance spot welding process. However, since aluminium does not have good spot weldability, for joints in car body frames, owing to considerations in terms of designs, too, a considerable number of methods have been tried, from resistance spot welding, arc welding such as MIG and TIG, and laser welding, to bonding, weld-bonding which uses both bonding and resistance spot welding methods together, mechanical fastening such as riveting and caulking, as well as rib-bonding which uses both bonding and mechanical joining methods, and, experimentally, friction stir welding. This means that almost all the joining methods employed for thin aluminium structures are involved in the production of car body frames. Therefore, this article will introduce the joining methods for body frames of cars as a study of the joining methods of thin aluminium alloys. Incidentally, aluminium materials characteristically used are very often extrusion moulded shaped sections and they sometimes have complex cross sectional dimensions. However, shaped sections used for automobiles are fundamentally for reducing weight, and consequently, they often consist of thin panels. Hence, problems for joining them are almost the same. Therefore, this article will deal with thin sheet materials and thin shaped sections together as thin aluminium alloys.