Abstract
Lightweight alloys can be considered among the most promising materials thanks to their capability to reduce the environmental impact, without affecting mechanical properties. In addition, when very complex shapes are required, a viable strategy could be represented by the adoption of non-conventional forming processes applied to tailored blanks that allow to obtain local variation of the material properties. In fact, referred to the Mg alloys, both grain size and temperature strongly influence the deformation behavior, as well as the mechanical properties. In this work, the effects of a selective Laser Heat Treatment (LHT) on a Mg AZ31B-H24 alloy sheet were investigated both numerically and experimentally. Experimental tests were performed, using a Diode laser source and keeping a square spot stationary in the center of the sample. The microstructure evolution was evaluated by means of light microscopy. Subsequently, the heat-treated samples were subjected to bulge tests under superplastic conditions (450°C) and using pressurized argon gas. The experimental microstructure distributions obtained were used for the numerical bulge tests analyses performed in the same conditions of the experimental trials. Experimental LHT results showed the capability to locally modify the microstructure when suitable temperatures and interaction times are selected. Regarding the bulge tests, the obtained results showed the possibility to effectively affect the thickness distribution of the final shapes.
Highlights
Products obtained via SuperPlastic Forming (SPF) have very good characteristics, due to the almost total absence of spring-back, which determines high shape accuracy
In order to quantify the discrepancy between the results deriving from Finite Element (FE) analyses and the ones obtained by the experiments conducted, for both variables adopted as output for the analyses the mean absolute percentage error (MAPE), was calculated
Considering the commercial AZ31B-H24 Mg alloy, the present work aims at evaluating the capability of a selective laser heat treatment to modify the microstructure of the sheet prior to a superplastic forming process at 450°C
Summary
Products obtained via SuperPlastic Forming (SPF) have very good characteristics, due to the almost total absence of spring-back, which determines high shape accuracy. Compared to conventional forming processes (i.e. stamping), SPF is quite expensive in terms of both energy consumption (elevated temperature are necessary to manufacture the components) and characteristic cycle times (superplastic properties occur at very low strain rates) [1] Irrespective to such drawbacks, SPF is attractive due to its ability to allow the manufacture of very complex shapes in a single step, eliminating or drastically reducing assembly and or stamping steps, allowing a comprehensive cost reduction. The adoption of materials such as Ti and Mg alloys for biomedical purposes pays particular attention to the issue linked to the thickness of the prosthetic implant; this aspect becomes of fundamental importance for the final characteristics of the implant, which must not be excessively rigid and, reduce osseointegration through stress shielding effects (Ti alloys) and have a thickness such as to guarantee its bio-absorbability in a controlled manner (Mg alloys) For this reason, the thicknesses must be accurately controlled for the implant to fully perform its repairing function [2,3]
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