Ultrasonic processing is known to be an efficient means of aluminium melt degassing and structure modification with additional benefits of being economical and environmentally friendly. This paper reports on the kinetics of ultrasonic degassing and regassing of foundry aluminium alloys and on pilot-scale degassing trials. Efficiency of ultrasonic degassing is compared with conventional Ar rotary degassing. Direct measurements of hydrogen concentration in the melt by Foseco Alspek-H probe are used along with reduced-pressure test. The effects of ultrasonic processing on porosity are studied using 3D X-ray tomography.

The formation of conventional metal-matrix composites reinforced with carbon nanotubes (CNTs) has proven difficult because of the agglomeration and inability of CNTs to disperse. We have explored the explosive consolidation of 150-lm aluminum powder/multiwalled carbon nanotube (MWCNT) aggregates (including multiconcentric fullerenes) at volume percentages of 2 and 5 pct. These consolidated mixtures formed two-phase, monolithic systems (TPSs) with the MWCNT aggregate material spreading along the Al grains and forming carbon phases mainly at the Al particle triple points. The Al powder particle (or grain) hardness increased from HRE 22 to HRE 40 for the consolidated Al, while the two-phase system hardness dropped from HRE 40 to HRE 39 and 33, respectively, for 2 and 5 vol pct MWCNT aggregate additions. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations illustrate a laminate-like structure of the consolidated MWCNT aggregate material, which is easily delaminated, causing intergranular (Al) failure. The Al grains exhibited a shock-induced dislocation substructure (0.5 to 3 lm) and recrystallized subgrains, which increased the individual particle/grain Vickers hardness from 24 to 43 HV.

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