Influence of Thermal Parameters, Microstructure, and Morphology of Si on Machinability of an Al–7.0 wt.% Si Alloy Directionally Solidified

Cássio A P Silva,Paulo M Júnior,Antonio L Moreira,Layo R M Leal,Otávio L Rocha,Emanuelle C Guimarães,Adrina P Silva

doi:10.1155/2018/9512957

Abstract

This study aims to correlate the influence of thermal and microstructural parameters such as growth rate and cooling rate (VL and TR) and secondary dendrite spacing (λ2), respectively, in the machining cutting temperature and tool wear on the necking process of the Al–7 wt.% Si alloy solidified in a horizontal directional device using a high-speed steel with a tungsten tool. The dependence of λ2 on VL and TR and dependence of the maximum cutting temperature and maximum flank wear on λ2 were determined by power experimental laws given by λ2 = constant (VL and TR)n and TMAX, VBMAX = constant (λ2)n, respectively. The maximum cutting temperature increased with increasing of λ2. The opposite occurred with the maximum flank wear. The role of Si alloying element on the aforementioned results has also been analyzed. A morphological change of Si along the solidified ingot length has been observed, that is, the morphology of Si in the eutectic matrix has indicated a transition from particles to fibers along the casting together with an increase of the particle diameters with the position from the metal/mold interface.

Highlights

It is well known that machining is one of the most important manufacturing processes in the metal-mechanical industry [1]. e improvement in the machining operation is related to obtaining components with the desired dimensions and satisfactory surface quality
Silva et al [41] investigated the effect of solidification thermal parameters on the macrostructure of an Al–7 wt.% Si alloy during the horizontal directional solidification under unsteady-state heat flow conditions and its correlation with cutting temperatures. ey have observed higher average cutting temperature for the columnar structure
In all cases, a signi cant temperature increase followed by a slight decrease at the end of the process

Summary

Introduction

It is well known that machining is one of the most important manufacturing processes in the metal-mechanical industry [1]. e improvement in the machining operation is related to obtaining components with the desired dimensions and satisfactory surface quality. Ese parameters influence the thermal conditions in which the phenomenon occurs, such as the displacement velocity of the liquidus isotherm (VL), temperature gradient (GL), and cooling rate (TR), which depend both on time and position relative to the metal/mold interface [14,15,16,17]. Such transient conditions, as well as the different compositions of the alloys, lead to various possibilities of obtaining final structures for the same melt and, for their mechanical performance

Al–Si Alloys

Results and Discussion

Conclusions e following major conclusions are derived from the present study: