Discussion on Differences in Determination of Hydrogen in Aluminum and Aluminum Alloy by Different Heating Methods

There was "secondary hydrogen" phenomenon in aluminum and aluminum alloys by pulse inert gas melting method (hereinafter referred to as the pulse method), which means, there was still a significant hydrogen release after reheating the measured sample. Domestic scholars tended to believe that the interference caused by the release of hydrogen from graphite crucibles, while Russia scholars tended to believe that the heating time was too short to completely extract hydrogen. In order to compare the different views, hydrogen in aluminum and aluminum alloys was determined by pulse method and thermal desorption method. The results were as follows: there were still obvious hydrogen released when the samples which was analyzed by pulse method were tested again by thermal desorption method, which meant "secondary hydrogen". The hydrogen reference materials GBW (E) 020030 certified value（0.19±0.04）×10⁻⁶（mass fraction,the same below）, GBW (E) 020030acertified value（0.24±0.06）×10⁻⁶, and GBW (E) 020031acertified value（0.25±0.05）×10⁻⁶ which were defined by the pulse method, were tested by thermal desorption method, and the results were 0.38×10⁻⁶, 0.58×10⁻⁶, and 0.71×10⁻⁶, with peaks located at approximately 450, 380, 460 ℃, respectively; The AlSi samples from different batches were simultaneously analyzed by pulse method and thermal desorption method, with results of 0.13×10⁻⁶, 0.16×10⁻⁶, 0.16×10⁻⁶ for pulse method and 0.70×10⁻⁶, 0.53×10⁻⁶, 0.48×10⁻⁶ for thermal desorption method, respectively. The release peaks were mainly located at 350 ℃ and 580 ℃. As shown by the above results, the testing results of thermal desorption method were generally higher than those of pulse method. Considering that the former used quartz tube heating, did not involve graphite crucible and slowly heated up, and the analysis time was measured in hours, it was preliminarily believed that the viewpoint that the heating time was too short to completely extract hydrogen, was more convincing. However, considering the widespread use of pulse method for determination of hydrogen in aluminum alloys in China, more detailed comparison and verification were still needed in order to obtain more convincing conclusions.