Esa Hiltunen

Prediction of Liquation Crack Initiation in Al-Mg-Si Alloy Welded Joints

Heat-treatable 6005-T6 alloy welded joints were studied experimentally and theoretically. The joints were gas tungsten arc and gas metal arc welded, bead-on-plate with 4043 and 5356 alloy filler metals. The temperature dependences of mechanical properties (yield stress, elastic modulus, thermal strain and characteristic ductility curve) under welding conditions were obtained using the 3800 Gleeble System. The unknown volume heat source parameters were found by application of inverse modeling. The three-dimensional heat conduction and thermomechanical problems were solved numerically. Liquation cracking criterion in terms of accumulated plastic strains was proposed. Strain vs temperature curves for the partially melted zone were calculated and compared with the ductility curve. The proposed technique allows the prediction of liquation cracking in arc welding of the 6005-T6 alloy.

Sensing in Aluminum Alloy Welding

With the emerging trends of automation of welding technology for high volume manufacturing and use of aluminum for lightweight construction, continuous efforts have been undertaken to improve sensing and data acquisition for automated welding of aluminum and its alloys. This work aims to present and compare various sensing methods i.e. touch sensing, through-arc seam tracking (TAST), vision and composite sensing for automated fusion welding of aluminum alloys. Sensing technologies used for sensing of the seam and weld process are analyzed with focus on difficulties specific to aluminum alloy welding. It is found that the automated welding of aluminum is a well-established subject and that solutions for most industrial automated aluminum welding needs can be developed by integrating ongoing advancement in the field of sensor technology.

Effect of Al2O3 film on the mechanical properties of a welded high-strength (AW 7020) aluminium alloy

The use in motor vehicles of lightweight metals such as aluminium and titanium provides a high strength-to-weight ratio, thereby lowering overall weight and reducing energy consumption and CO2 emissions. Aluminium alloys have thus become an important structural material especially high strength and ultra-high strength alloys such as AW 7020. Many studies have shown that the presence of an aluminium oxide (Al2O3) thin film formed naturally on aluminium alloys is detrimental to welding. This article further investigates the specific effect of the Al2O3 thin film on welding AW 7020 alloy. An analytical experiment of welded AW 7020 alloy using a pulsed metal inert gas (MIG) robotic weld machine is carried out. Four specimens were cut, butt welded, and examined. The weld parameters included pre-weld cleaning of the Al2O3, pre-, and post-weld heat treatment. Al2O3 was removed by wire brushing; preheating was conducted at a temperature of 130 °C; and natural ageing was conducted by post-weld heating at 480 °C for 2 h, followed by quenching in water at 90 °C for 8 h, reheated, and sustained at 145 °C for 15 h. The result shows that the presence of Al2O3 layer appears not to be detrimental to the weld with new welding technologies, therefore suggesting that it is not necessary to grind off the Al2O3 layer before welding. This finding implies that welding costs can be lowered and weld quality improved when new welding technologies are applied in the welding of high-strength aluminium alloys.

Real-Time Weld Process Monitoring

Welding defects result infailure of the machinery and other negative consequences. Therefore, they need to be detected as they appear to ensure efficient and high-quality production. There is a raising interest in the implementation of sensors to provide highly accurate and robust real-time welding process monitoring. This work describes the four most widely used techniques of welding process monitoring. These monitoring techniques are arc sensors, optical sensors, infrared sensors, and ultrasonic sensors. This work explains their principles of operation: discuss their advantages and limitations and give typical areas of application. Arc sensors, optical sensors, infrared sensors, and ultrasonic sensors are described in detail with the necessary figures and schemes in the first part of the present study. The physical background, the strengths and weaknesses, and real life examples of the sensing techniques are given in this part. The results of the research show that each sensing method has its specific features thatcan play an important role in certain welding applications. Arc sensors do not requireadditional equipment in the welding zone. Thisis why they can be used where operational space is limited. Optical sensors allow the observation of the weld pool behavior. Infrared sensors can create the temperature profile of the weld. Ultrasonic sensors usually have good resolution and can provide accurate data. This paper will help welding engineers to choose the optimal sensing equipment for aspecific industrial application.

Hot Cracking Susceptibility of Wrought 6005 and 6082 Aluminum Alloys

Hot cracks can easily be produced in the welding of aluminium 6000 series if the welding conditions and welding procedures are not carefully controlled. The aim of this study is to examine both theoretically and experimentally some of the factors that cause hot cracks and how to minimize or avoid this undesirable outcome when welding 10 mm thick heat treatable wrought aluminium alloys 6005-T6 and 6082-T6 bead-on-plate using 4043 and 5356 alloy filler metal by mechanised gas tungsten arc (GTA) and gas metal arc (GMA) welding processes. The welding process, filler metal composition and preheating temperature have been chosen as the main factors affecting the formation of hot cracking. A comparison of these welding processes will be made based on heat input (Q). The influence of different factors on sensitivity to cracking is evaluated by preparing macro and micro photos of the test samples, and Vickers hardness tests were used to examine the extent of cracks formed and the degree of the loss of hardness. It has been shown in experiments that specimens welded with 5356 alloy filler wire are more prone to hot cracking than those welded with 4043 wire, and GMAW shows less cracks than GTAW due to its lower heat input. The effect of preheating proves to have little or no consequence.