Abstract
The effects of degassing, holding time and melt additions (Sr, Sr + Ti, Ti, B and B + Sr) on the quality of A356 melts were examined. A total of 120 reduced pressure test samples were collected. Pores in these samples were analyzed via digital image processing to determine the number density of pores as well as the statistical distribution of their sizes. Results showed that in all cases, degassing with argon reduced the number of defects regardless of the additions made to the melts. Moreover, all additions were found to degrade melt quality. The lowest number density of pores in all melts was achieved in melts with no additions that were degassed. In both degassed and non-degassed melts, Sr additions degraded the melt quality significantly. The mechanisms of melt quality improvement or degradation with different melt treatments are discussed in the paper.
Highlights
Cast Al-Si-Mg alloys display a good combination of corrosion resistance and castability, in addition to their high strength to density ratio
Al-Ti5-B1 and Al-3B alloys were added into liquid A356 for grain refinement to obtain a concentration 10 ppm Ti or 10 ppm B
If the melt is not degassed after Sr addition, the melt should be the if the melt is not degassed after the
Summary
Cast Al-Si-Mg alloys display a good combination of corrosion resistance and castability, in addition to their high strength to density ratio. Irregular or tortuous pores have been attributed to negative pressures developed during solidification To overcome this type of porosity, researchers [3,4] investigated feeding mechanisms in castings and the efficiency of different types of feeders. Melt treatments such as grain refining and Si eutectic modification have been studied to obtain a microstructure in cast Al-Si alloys to alter the microstructure and minimize the detrimental effect of pores on mechanical properties. Similar results were found by Iwahori et al [25] who investigated the effect of Sr additions on porosity formation in Al-7%Si alloys They reported that there was a correlation between the number of oxides in the melt and porosity for Sr modified A356. When the oxide content was high, Sr addition followed by vacuum degassing did result in increased porosity
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