Michinori Okubo

Effects of filler metals on the properties of 7175 aluminium alloy electron beam welds

Summary In electron beam welding of 7175 aluminium alloy plates of 15 mm thickness, the effects of filler (insert) metals on the properties of welds have been investigated by microscopic observation, electron probe microanaly‐sis, and hardness, tensile and impact tests. Hardness of welds without the insert is almost recovered by T76 post heat treatment. Hardnesses of weld metals with A1100 and A5052 inserts are lower than those of the base metals. Grain size in the weld metal from butt welds made without inserts is larger than from butt welds with inserts of A1100 and A5052 in thin plates with thicknesses of 0.5 mm and 1.0 mm. Segregation of Mg is found in the weld crack zone. In the case of A5052 insert metal, the formation of cracking is suppressed and thus the joint efficiency of welds is improved to about 90%. Whilst the absorbed impact energy of welds made without an insert shows a lower value than that of the base metal, toughness of the welds is improved by using A5052 insert metal.

Formation behaviours of blowhole and chill layer by GTAW in cast iron

ABSTRACT Cast irons have some excellent characteristics in wear resistance, vibrational damping etc., and are widely used in many industrial machinery applications. But, the weldability has been much inferior originated from its high-carbon content. Several researches have reported that some of the important factors affecting the weldability were formation of blowhole and chill layer during fusion welding and subsequent rapid cooling. In this study, the formation behaviours of those were investigated in both flake and nodular graphite cast irons. Tungsten inert gas arc welding was performed using several kinds of filler metal varied nickel and chromium content. The study was made by paying attention to carbon behaviour and influence of nickel and chromium in filler metal on it. Experimental results obtained were as follows. The amount of blowhole increased with nickel content and decreased with chromium content. On the other hand, the amount of chill layer increased with chromium content and decreased with nickel content. It was estimated that both blowhole and chill layer formation were related to activity and diffusivity changes of carbon affected by nickel and chromium content. Then consequently they have a correlation relationship each other.

The quality evaluation of advanced plasma welding technology

In order to establish a welding technology with excellent stability, efficiency, and quality assurance for the welding of thick sheets of aluminium and other non-ferrous metals, we have developed a new high-current plasma welding machine (‘the new machine’) which is cheaper and has a wider range of use than laser welding and electron beam welding. This is a joint business-university research and development project, which is part of the ‘Strategic Project to Support Technological Enhancement’ (Supporting Industry), a policy for the support of small and medium enterprises carried out by the Ministry of Economy and Industry. This study comprised tests to achieve concentration of energy density, the establishment of a method of optimal current waveform control by simulation, optimization of torch shape by simulation of high-speed plasma current, and optimization of control methods for a total welding system using robots and of welding methods. In this paper, we report on the assessment of the new plasma welding method and the results of measurement of the temperature of the molten metal by an immersed optical fibre thermometer.

Dissimilar aluminium weldability of SiC particle reinforced aluminium alloy to Al–Si, Al–Mg, Al–Mg–Si, Al–Zn–Mg–Cu alloys by electron beam welding

The SiC particle reinforced aluminum alloy has been developed for various machine parts. Aluminum welded machine parts often require welded joints composed of dissimilar alloys. In the present study, electron beam weldability of dissimilar joints was investigated on different combinations of aluminum alloys of 10 mm thickness. The main alloy is 10% SiC particle reinforced Al–Si aluminum alloy. Combination wrought alloys are Al–Si, Al–Mg, Al–Mg–Si and Al–Zn–Mg–Cu alloys. The electron beam machine is a 6 kW high voltage type. The joint groove is of square butt without filler metal. In the case of SiC reinforced alloy/Al–Si and Al–Mg, joints, weldability was poor because some weld imperfections were recognized such as arcing and other defects. In the case of SiC reinforced alloy/Al–Mg–Si, Al–Zn–Mg–Cu, the cracking sensitivity is low while some small porosity was recognized. Tensile strength became about 150 MPa such as SiC reinforced alloy. Impact values of the SiC reinforced alloy/Al–Mg–Si joint were recovered through 2160 h room temperature ageing. Micro segregation of the Si element was recognized for the SiC reinforced alloy/Al–Mg–Si joint by electron probe microanalyser analysis.

Properties of dissimilar joints for nano-structure aluminium alloy to aluminium-based alloys by electron beam welding

Reasons for widespread use of aluminium alloy structures include high strength and weight reduction. Also, investigation from various perspectives, such as joining method and development of the parent material are being considered for improvement of weld ability of high strength aluminium alloys, currently considered difficult to weld. This research is the application of an electron beam welding method that has high density energy to nano-structure high strength aluminium alloys and dissimilar aluminium alloys. The nano-structure high strength aluminium alloy1 that we have focused on has an intermetallic compound that is dispersed with a high volume fraction and that is expected to be applied in numerous industries. There have been interesting results obtained from fundamental and useful research2 of TIG welding for Al–Mg systems and Al–Mg–Si systems with regards to welding of dissimilar aluminium alloys. In this test, an electron beam heat source considered to have low actual weld heat input was used. A nano-structure high strength aluminium alloy with a plate thickness of 10 mm was used as the primary parent material. The alloys Al–Si systems, Al–Mg systems, Al–Mg–Si systems, and Al–Zn–Cu systems were used as the alloy combinations for dissimilar metal joints and two to three investigations were made in order to obtain fundamental knowledge.

Technical guide of electron beam welding and experiments of dissimilar aluminium joints

The electron beam welding heat source, capable of delivering controlled high density energy, is applied to a range of materials and contributes to the enhancement of production technology in many sectors. The most vibrant time in the utilisation of electron beam welding machines is generally said to be about 1948.1 During this period, the application had been promoted for nuclear reactor fuel pipe materials (Nb, Ta, Zr, V, Mo, W and alloys of these) which are active metallic materials. Due to improved electron beam welding machines, utilisation was accelerated for the application to aluminium and its alloys. In this paper, the technical information, including technical word-of-mouth tradition and the characteristics of joints made between dissimilar aluminium alloys, are outlined from aspects of electron beam welding machine operation.

Dissimilar joints between Al-Mg A5052 wrought alloy and AC7A castings made by electron beam and gas tungsten arc welding

Summary This paper describes a fundamental investigation of the weldability of A5052 wrought alloy and AC7A castings in electron beam welding and gas tungsten arc welding. Microscopic observations, hardness, tensile, and impact tests were used. In electron beam welding, the tensile and impact properties of the wrought alloy weld metal and heat affected zone are satisfactory. Micro-solidification cracks are found in the weld metal, whereas micro-liquation cracks are found in the AC7A HAZ. The tensile properties of the welds produced by GTAW (or TIG) are virtually equivalent or slightly inferior to those of the electron beam welded joints.

Partial modification of an aluminium wrought alloy and casting by a gas tungsten arc heat source: Applicability of modification to an internal thread

Summary Partial modification of an internal thread in an Al-Zn-Mg wrought alloy (T651) and Al-Si-Mg casting (F) has been investigated using a gas tungsten arc heat source and a copper alloying process. Threading was machined into the partial modification zone and the mechanical properties of the internal thread were evaluated by a hexagon-head-bolt tensile test. With the Al-Zn-Mg wrought alloy, the hardness distribution of the modified zone became uneven and grain boundary cracks were recognised in the modified zone. With the Al-Si-Mg casting, hardness at the modified zone increased with an increase in copper addition. Improvement in the tensile strength of the internal thread was confirmed by relevant process parameters.

Narrow gap automatic gas shielded arc welding of high carbon steel

Summary Rail steel is a typical high carbon material and has previously been extensively researched to improve its weldability. This paper describes an investigation of narrow gap automatic gas shielded arc welding of rails to determine the effects of the process parameters, weld metal carbon content, and post weld heat treatment through observations of defects and microstructures, hardness measurements, and tensile tests of welded joints. Through adjustment of the temperature of the water-cooled copper block surrounding the rail welds, the heat input to the base material can be controlled and the weld quality thus improved. Suitable post weld heat treatment and welding conditions improve the weld properties. Control of the weld metal carbon content is an important factor in prevention of hot cracking. Hot cracking in the HAZ is influenced by MnS inclusions and can be prevented through application of suitable process parameters.