| The concentration of hydrogen is one of the most important parameters in liquid aluminum processing because it is responsible for gas porosity which affects casing quality, ie. pressure tightness, mechanical properties etc. In order to gain optimum quality, the amount of hydrogen dissolved in liquid aluminum must be known prior to casting. This has led to the development of several techniques to quantify hydrogen in liquid aluminum. Among these is the Reduced Pressure Test (RPT). The RPT is simple, very inexpensive and commonly used in aluminum foundries to obtain a qualitative evaluation of the melt hydrogen level.;In this thesis the development of the RPT to a truly quantitative level is discussed. This includes redesigning of the steel mold and the application of a riser. The mold was redesigned to improve the test sensitivity while a CO;Several parameters that affect the test sensitivity and reproducibility were studied, such as chamber pressure, amount of inclusions, pouring temperature, and mold temperature. It was found that there are two important parameters that strongly affect the test; chamber pressure and amount of inclusions. The lower the chamber pressure the better the test sensitivity but the poorer the test reproducibility. Increasing the amount of inclusions improves the test sensitivity.;The constant volume sample can be used to predict the amount of hydrogen in the melt for various types of alloys including 319, 356, 357 and 413 within a reasonable margin of error. The error as measured by this technique was found to be in the range of ;A simple mathematical model based on a mass balance approach was developed to calculate pore size and sample density. The model predicts the density accurately for various types of alloys and different melt treatments. |
