Larry A. Godlewski

EFFECTS OF N ON CREEP PROPERTIES OF AUSTENI-TIC HEAT-RESISTANT CAST STEELS DEVELOPEDFOR EXHAUST COMPONENT APPLICATIONSAT 1000 ℃

To comply with more stringent environmental and fuel consumption regulations in recent years, automotive gasoline engines equipped with turbochargers are increasingly used to improve fuel efficiency. As a result, exhaust gas temperatures are now reaching 1050 °C, about 200 °C higher than the conventional temperature. Hence, there is an urgent demand in automobile industries to develop novel and economic austenitic heat-resistant *福特与中国大学合作研究资助项目 收到初稿日期: 2015-12-03,收到修改稿日期: 2016-03-03 作者简介:张银辉,男, 1985年生,博士生 DOI: 10.11900/0412.1961.2015.00618

Using quality mapping to predict spatial variation in local properties and component performance in Mg alloy thin-walled high-pressure die castings: an ICME approach and case study

This paper explores the use of quality mapping for the prediction of the spatial variation in local properties in thin-walled high-pressure die castings (HPDC) of the magnesium alloy AM60. The work investigates the role of casting parameters on local ductility and yield strength and presents a model for predicting local ductility and yield strength in a cast component. A design of experiment (DOE) was created to examine the role of various casting parameters on local properties such as ductility and yield strength. Over 1,200 tensile samples were excised from cast parts and tested. Casting simulations were also conducted for each experimental condition. Local properties were predicted, and the local property (quality map) model was compared with a prototype production component. The results of this model were used as input to a performance simulation software code to simulate the component-level behavior under two different loading conditions. In this study, the authors bypassed the traditional Integrated Computational Materials Engineering (ICME; process-microstructure-properties) approach in favor of a semi-empirical quality mapping approach to provide estimates of manufacturing sensitive local properties for use in process and component design.

The Dimensional Stability of Cast 319 Aluminum

The automotive use of cast aluminum has greatly increased during the past decade, especially for engine blocks and cylinder heads. One physical property that is important in elevated-temperature applications is longterm dimensional stability of the cast aluminum component. Certain cast aluminum alloys (like 319) can undergo dimensional changes when exposed to engine operating temperatures over long periods of time; when these changes occur, the shape of the casting is distorted and the performance of the component may be diminished. Thus, a study was conducted to measure dimensional growth changes in a cast 319-type aluminum alloy as a function of heat-treatment, exposure temperature, and exposure time at the given temperature. The results show that all three factors have a significant effect upon the dimensional stability.

Role of Pore Size Distribution in Ultrasonic Characterization of Microporosity in Aluminum Castings

Microshrinkage porosity in cast aluminum plates was characterized utilizing the frequency dependence of ultrasonic attenuation caused by pore scattering. The back‐surface echo spectral shape was fitted assuming various size distributions of spherical pores. Best fits were obtained for a lognormal distribution. Pore volume fraction inferred from these fits overestimates the actual volume fraction by a factor related to the complicated, nonspherical pore shapes. These results permit accurate, nondestructive laboratory measurements of porosity with 2‐mm spatial resolution.

Inferring pore size distributions in cast metals from ultrasonic attenuation

The frequency dependence of ultrasonic attenuation in cast metals has previously been shown to contain information about the volume fraction and size of pores. While direct metallographic examination shows that the actual size distribution can be quite broad, previous investigations have analyzed ultrasonic attenuation data on the assumption that all pores have the same, or nearly the same, size. That restriction can be eliminated by analyzing the data using the concept of maximum entropy. Pore sizes are divided into discrete bins, each containing a fraction fi of all the pores, and the entropy, obtained by summing −fi ln(fi) over all bins, is maximized subject to the constraints of the frequency‐dependent attenuation data. The resulting pore size distributions for cast aluminum samples containing various levels of porosity are often found to be approximately log‐normal. Volume fractions of pores deduced from these distributions are in excellent agreement with determinations using the Archimedes method.