Investigating the influence of manufacturing parameters on machinability of aluminum foams produced through powder metallurgy route


Thesis Type: Doctorate

Institution Of The Thesis: Bursa Uludağ University, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2014

Thesis Language: Turkish

Student: CİHAT ENSARİOĞLU

Supervisor: Mustafa Cemal Çakır

Abstract:

Closed cell aluminum foams are new generation materials that are attractive to scientific community and technological applications (commercial-military) because of their high degrees of strength-to-weight ratio, ability to absorb mechanical energy, capacity of sound and heat insulation, melting temperature (with respect to materials like polymeric foams), recycling ratio. In this study, foaming and machining of alloyed aluminum foams (850 and 7075) produced by powder metallurgy route were investigated. On foaming studies, in the section in which the simulation of matrix material was performed, JMatPro was employed to analyze the melting-solidification stages. In experimental section, first, the effect of manufacturing factors on morphological characteristics (expansion ratio, average cell area, circularity, section homogeneity), which affects material properties and some of which were found by image analysis (with ImageTool), were examined and optimized. Secondly, the effect of alloying elements on expansion ratio and section homogeneity was determined. In foaming, Minitab was utilized when designing the experiments (Taguchi, response surface methodology -RSM-, mixture) and analyzing the results. The foams were subjected to XRD qualitative phase analysis, SEM-EDX mapping, SEM imaging, micro-hardness measurement. On machining studies; first, some machining factors (cutting tool type, cutting speed, feed per tooth) were examined, secondly, trials were made with varying alloying elements ratios; and machinability was interpreted in a qualitative manner (smearing on workpiece and tool, tool wear). In Taguchi experiments, for 7075 and 850; the most important factors were revealed as blowing agent percentage, secondary consolidation pressure, expansion temperature and time. For 850, the lower the initial furnace temperature the better the macro-structure was. For 7075, a linear model was obtained with RSM, with which foaming factor value recommendations for desired levels of quality characteristics can be drawn and also reductions on foaming agent percentage can be generated. For 850 (in a way that it can also be interpreted by phase simulation analyses); it was observed that Cu is the key element for expansion ratio and Ni was for section homogeneity. In 850-referenced alloys, phases of CuAl2 were encountered in XRD, SEM, SEM-EDX mapping analyses although the workpieces were water-cooled. The micro-hardness values for 850-referenced alloys were 40-60 HV0,1. In machining experiments; it was seen that increased cutting speed enhanced the chip smearing on tool flank face, while increased feed decreased it. For all the alloys studied, no smearing on workpiece was observed.