Hydrogen micro pores in cast aluminum alloys

According to our extensive 3-D non-destructive observations for various kinds of cast aluminum alloys, high-density micro pores have been identified to exist in all of the aluminum alloys except pure aluminum. The observation has been performed with the largest synchrotron radiation facility in the world, SPring-8. Growth/shrink and formation! annihilation behaviors of each micro pore are tracked during heat treatments and a plastic forming process. It has been clarified from the quantitative analysis of 3-D images that the micro pores exhibit the Ostwald ripening during the heat treatments. It has been found that considerable amount of hydrogen contained in the cast aluminum alloy is trapped in micro pores, while it is quite limited in a pure aluminum. Various efforts have been reported to eliminate such micro pores. Annihilation behaviors of micro pores under shot peening are demonstrated in 3-D. Since usually the porosity acts as fatigue crack initiation sites and fatal defects under tension, this information would be beneficial also from an industrial point of view. We also reports how mechanical properties of the cast aluminum are degraded due to the existence of micro pores in this review paper. Especially it is noteworthy that the ductile fracture of aluminum alloys is dominated by micro pore growth in addition to particle damage that is conventional text-book knowledge. Copyright