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Permanent mold castings of high purity binary Al-Si alloys (Si: 3, 7, 12 and 20%) were tested. The fatigue crack propagation in as-cast alloys in the Paris regime is seriously influenced by Si concentration less than eutectic composition. Al-20%Si alloy is less stable in fatigue crack propagation than the other alloys. Solution treated high Si alloys show slower rates of fatigue crack propagation than as-cast alloys. The fact depends on strengthening of the matrix, forming of eutectic Si particles into spheres and on increase in crack closure. The resistance to fatigue crack initiation is improved by high content of Si in as-cast alloys and by solution treating.

Arc jets that spout from electrodes as a result of high-current fault arcs cause damage to the surrounding apparatus. This paper describes the results of the spectroscopic observation of arc jets of 10-50 kA rms ac arcs at the current peak. The electrodes were copper of 40 mm in diameter, and the gap length between the electrodes was 3.4 m. The temperature and the copper vapour concentration of the arc jet were determined by considering the self absorption of two spectral lines. As the arc current increased from 10 kA to 50 kA, the temperature did not change greatly (10 000-11 000 K), and the maximum copper vapour concentration (molar rate) in the arc jet increased from 0.03% to 3%.