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Mechanical strength of Fe/Al structural transition joints subject to thermal loading

Tricarico L., Spina R.

Archives of Materials Science and Engineering

2009

Vol. 37, nr 2

85-93

Purpose: The aluminum/steel structural transition joints (STJs) are widely used in shipbuilding industry due to the advantages of joining these two materials with important weight savings while exploiting their best properties. The research objective is the evaluation of mechanical strength of explosion welded structural transition joints by imposing severe thermal loads in specific temperature ranges. Design/methodology/approach: Mechanical characterization of heat treated specimen have been performed to evaluate the influence of these thermal cycles on final joint resistance and evaluate the product in service. Several specimen aluminum/steel joints have been heated at specific temperature and time and air-cooled in compliance with a Central Composite Design (CCD) experimental plan to investigate the influenced of these factors on inter-metallic layers. Findings: The micro-hardness measurements have been pointed-out that the hardness of the inter-metallic compounds decreased with the temperature (values greater than 300°C). The processing time influence has been less significant in the observed temporal ranges. This trend has been also confirmed by evaluating the maximum strength of the bond Fe/Al interface. None of the specimens exhibited significant strength variation for thermal loads with temperature lower than 300°C, independently from the processing time. Research limitations/implications: This methodology is very useful to perform acceptance controls of STJ before use. Practical implications: These observations are very important to suggest the application of laser techniques to weld this type of joints, thanks to the very narrow localized thermal input. Originality/value: The paper presents an alternative and cheap way to assess quality of STJs from the mechanical point of view.

Numerical and experimental analysis of the Warm Deep Drawing process for Mg alloys

Palumbo G., Sorgente D., Tricarico L., Zhang S. H., Zheng W. T.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 14, nr 1-2

111--118

Purpose: The present work is aimed to investigate the Deep Drawing process of Mg alloy sheet in Warm conditions, since through the temperature temperature the number of independent slip systems of the Mg alloys can be enlarged. Design/methodology/approach: A FE model and an equipment for warm deep drawing tests were created, since an experimental-numerical method was adopted; the most efficient heating positioning and the most suitable way of performing the WDD process was evaluated using data coming from the numerical model and temperature and punch load acquisition coming from experimental activity. Findings: Limit Drawing Ratio (LDR) equal to 2.6 for AZ31 Mg alloy (cross rolled, thickness 0.6mm) was obtained at the temperature 170oC using heater embedded in the female die; Drawing Ratio equal to 3.1 for the same Mg alloy (thickness 0.6mm) was obtained setting the temperature of the blank holder at 250oC (throughout heaters embedded in it) and cooling the central part using a water cooled punch. Research limitations/implications: Next step of the research will be to evaluate the optimal value of process parameters (speed, temperature and blank holder pressure) in order to draw the process window. Practical implications: The process with controlled heating and cooling technology can be applied in industrial production of a wide range of Mg alloy parts (structural components, covers for computer, communication and customer electronic, sportive equipments). Originality/value: Specific heating and cooling system were designed to analyse the influence of the different heating strategies combined with or without punch cooling on the WDD of AZ31 Mg alloy sheets.