Chih-Kuang Lin

Effect of trace Ce addition on the microstructures and mechanical properties of A356 (AL–7SI–0.35 Mg) aluminum alloys

A356 hypoeutectic alloy is a heat-treatable Al–Si–Mg system with a normal composition of Al–7 wt.% Si and about 0.35 wt.% Mg which has seen widespread applications in the aerospace and automotive industries. The purpose of this study is to determine the influence of different amounts of Ce on the microstructures and mechanical properties of A356 alloys. The findings indicate that modification efficiency in microstructures and mechanical properties of A356 alloy are greatly enhanced by adding 1.0 wt.% Ce. Two kinds of intermetallic compounds are found in the study, including Ce–23Al–22Si and Al–17Ce–12Ti–2Si–2 Mg (in wt.%) phases. Moreover, though the ductility of the Ce modified alloys are both greatly improved, there is no positive effect on the ultimate tensile strength that can be attributed to the formation of an Al–17Ce–12Ti–2Si–2 Mg phase. Furthermore, the results of thermal analysis reveal that there is no direct relationship between eutectic growth temperature and silicon morphology/modification rating.

Effect of rare earth elements addition on microstructures and mechanical properties of A356 alloy

Abstract A356 is a heat treatable Al–Si–Mg hypoeutectic alloy with a normal composition of 7 wt‐%Si and ∼0·3 wt‐%Mg which has widespread applications in the aerospace and automotive industries. The influence of the rare earth metals La and Ce on the microstructures and mechanical properties of A356 alloy has been investigated. The findings indicate that the modification efficiency of 1 wt‐%La is similar to that achieved by commercial modification with 0·02 wt‐%Sr, but the modification efficiency of Ce is lower than those of La and Sr. Two kinds of La or Ce rich intermetallics are found in this study: AlTiLa(Ce)Mg and AlSiLa(Ce) phases. Although the ductility of the rare earth modified alloys are both greatly enhanced, no positive effect on ultimate tensile stress that can be attributed to the formation of AlTiLa(Ce)Mg phase was observed.

Stress Analysis for a Substrate Holder Module and Thin Films Grown in an MOCVD Reactor

The aim of this work is, using finite element analysis, to study the effects of thermal load and rotation speed on the structural integrity of a substrate holder module in an MOCVD reactor. Several loading conditions are considered, including thermal load and rotational speeds of 0-1500 rpm. In addition, the wafer bow and residual stress of GaN film grown on silicon or sapphire wafer are systematically studied. Simulation results indicate the variation of critical stress with rotation speed in all of the components is small. Given a similar heat source in the MOCVD reactor, temperature of the upper components such as susceptor, substrate holders, and wafers is higher in the case of sapphire wafer than that in the case of silicon wafer. The temperature gradient of upper components is greater for the silicon wafer case. A greater temperature gradient in the film-substrate system generates a greater wafer bow and residual stress in the grown thin film. Therefore, temperature uniformity is an important parameter for the epitaxial process. The sign of residual stress is different between a GaN film grown on a sapphire wafer and a silicon wafer (compressive for sapphire wafer and tensile for silicon wafer). For growing a GaN thin film, sapphire wafer is better than silicon wafer in terms of lessening cracking in film.

Notch Effect on the Corrosion Fatigue Behavior of an Austenitic Stainless Steel

The objective of this study is to characterize the influence of notch effect on the high-cycle corrosion fatigue properties of AISI 347 stainless steel in various environments, namely, air, water, NaCl, NaCl plus inhibitor, and H2SO4 solutions. For smooth-surface and semi-circular notch specimens, the rank of fatigue strength in all of the given environments generally took the following order: air ≈ salt water plus inhibitor > deionized water > salt water > sulfuric acid solution. For V-notch specimens, the S-N curves were separated into two groups, i.e. one with air and 3.5% NaCl plus inhibitor and the other with deionized water, 3.5% NaCl and H2SO4. This was attributed to a greater effect of localized acidification occurring at the root of V-notch as compared to the smooth surface and semi-circular notch.