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S18 Processos Mecânico-Metalúrgicos |
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Title:
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PRODUCTION OF RHEOCAST SLURRIES BY PARTIAL MELTING THROUGH ALTERNATIVE THERMOMECHANICAL TREATMENTS
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Summary :
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ABSTRACT. THE PRODUCTION OF ALLOYS WITH RHEOCAST STRUCTURE, IN WHICH THE PRIMARY PHASE CONSISTS OF GLOBULAR PARTICLES, BY PARTIAL MELTING, INVOLVES GRAIN RECRYSTALLIZATION AND SECONDARY PHASES MELTING. IN THE PROCESS KNOWN AS SIMA ( STRAIN INDUCED MELT ACTIVATION), THE RAW MATERIAL IS COLD DEFORMED BY ROLLING IN TWO STEPS, MAKING IT LESS EFFICIENT. THIS WORK INVESTIGATES THE PRODUCTION OF RHEOCAST AL-3.35WT%CU ALLOY BY ALTERNATIVE THERMOMECHANICAL TREATMENTS. TWO TREATMENTS ARE PERFORMED: RECRYSTALLIZATION AND PARTIAL MELTING (RAP) AND OVERAGING (OAT) PROCESSES. IN THE FIRST, AS-CAST DENDRITIC ALLOY IS COLD-DEFORMED AT ROOM TEMPERATURE AND THEN HEATED TO A CONSTANT TEMPERATURE IN THE MUSHY ZONE, TO OBTAIN THE RHEOCAST STRUCTURE. IN THE SECOND, THE ALLOY UNDERGOES A SOLUTION AND PRECIPITATION HEAT TREATMENTS, BEFORE COLD-DEFORMATION, WITH THE AIM OF OBTAINING PRECIPITATED PARTICLES OF SECONDARY PHASE WITH SIZE AND INTERPARTICLE SPACING FAVOURABLE TO INCREASE THE NUCLEATION RATE OF RECRYSTALLIZED GRAINS DURING HEATING OF THE ALLOY. RESULTS SHOW THAT THE TWO ROUTES PRODUCE GLOBULAR STRUCTURES, WITH GRAIN SIZE REDUCTION OF 700 AND 900% FOR RAP AND OAT, RESPECTIVELY, WITH RESPECT TO INITIAL GRAIN SIZES. IN GENERAL, OAT PROCESS RESULTS IN MORE ROUNDED AND SMALLER GLOBULES IN THE RHEOCAST STRUCTURE THAN RAP. |
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Author :
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Margarido, Marcos 0
Robert, Maria Helena
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Paper View :
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