The influence of process parameters on the shrinkage cavity and porosity in the semi-solid die casting process was studied by using the control variable method, and the causes were analyzed on the basis of empirical theory.
(1) The shrinkage cavity and porosity defects in the experiment all appear in the final solidification region shown in the solidification simulation, which is the axial region of the cylinder this time.
(2) When the pressure is 200 bar-loobar, the shrinkage cavity and porosity decrease with the increase of the pressure. The lower pressure (200bar) will lead to significant shrinkage defects in the sample, especially in the upper part of the sample. With the increase of pressurization pressure (500bar-800bar), the shrinkage and porosity defects of the samples are obviously improved, and the distribution range is greatly reduced. When the pressure is increased to looobar, the shrinkage defects disappear and there are no defects under fluorescence analysis and metallographic observation.
(3) When the handle thickness is 16 mm-68 mm, the shrinkage cavity and porosity decrease with the increase of the handle thickness. The smaller handle thickness (16 mm) will lead to significant shrinkage and porosity defects in the sample. With the increase of the handle thickness (32 mm-42 mm), the shrinkage cavity and porosity defect of the sample will be obviously improved, which is basically changed from large area shrinkage porosity It is a local small shrinkage cavity, and the distribution range is greatly reduced. When the handle is thickened to 68mm, the shrinkage cavity and porosity of the sample disappear, and there are no defects under fluorescence analysis and metallographic microscope observation.
(4) When the mold temperature is between 50 ° C and 230 ° C, the shrinkage cavity and porosity of the sample decrease gradually. The lower mold temperature (50 ° C) will lead to significant shrinkage and porosity defects in the sample, and a large area of shrinkage porosity will be produced in the upper part of the sample. With the increase of mold temperature (140 ° C), the shrinkage cavity and porosity of the sample can be significantly improved 。 Basically, the shrinkage porosity changes from large area to local small shrinkage cavity, even disappears and the distribution range is greatly reduced. When the mold temperature rises to 230 ° C, the shrinkage and porosity defects disappear, and there are no defects under fluorescence analysis and metallographic microscope observation.
(5) Under the experimental conditions, the pressurization pressure is looobar, the material handle thickness is 68 mm, and the mold temperature is 230 ° C. the cylindrical sample without shrinkage cavity and porosity under metallographic observation can be produced stably. The diameter of the thickest area of the sample is about 30mm.