Welding Journal - April 2012 - (Page 14)

ALUMINUM Q&A Q: I am interested in the fracture characteristics of aluminum alloys. I have heard varying comments on the subject of Charpy impact testing of aluminum. How are toughness levels determined for aluminum, and how does welding aluminum affect its toughness? BY TONY ANDERSON stressed material) rarely occurs under any conditions. For these alloys, the meritrating approach is generally sufficient, and measures of notch toughness or tear resistance providing relative qualitative ratings may be sufficient. However, there are a number of higher-strength aluminum alloys and tempers that are used principally in aerospace applications, where strength must be used to the maximum advantage and the consequences of unexpected lowductility failure must be considered. For these particular alloys and tempers, more precise evaluations of toughness by methods such as fracture toughness testing are required for quantitative evaluation of fracture behavior under specific service conditions and, subsequently, the design of fracture resistance into the structure. ance to fracture (the ductile to brittle transition range), brought about the development of various tests to determine this characteristic. The Charpy and Izod notched-bar impact tests as well as the drop-weight tests are among those widely used for this purpose. The significance of these tests is to establish the temperatures below which precaution must be taken when using materials that have such a sudden change in their fracture behavior, typically in low-temperature applications. Aluminum alloys, like other facecentered cubic materials, do not exhibit any sudden transition in fracture characteristics with a decrease in temperature. Furthermore, many aluminum alloys are so tough at very low temperatures that they do not fracture completely during this type of testing and produce test results that are of no significant use. For these reasons, the notched-bar impact tests, such as the Charpy, have never been considered useful indicators of the fracture characteristics of aluminum alloys. For these same reasons, aluminum filler metals have no requirements for impact testing. A: With the continued development and use of high-strength aluminum alloys in critical components used in aerospace, automotive, marine, and cryogenic applications, the ability to predict their fracture resistance is important. Some of the areas where consideration of this characteristic is particularly useful are as follows: Alloy development (determining which alloys and tempers of a given group have the greatest fracture resistance); alloy selection (making decisions on alloy choices for specific applications); and design (establishing safe design stresses and/or predicting critical crack or discontinuity sizes under specific service conditions). Most commercial aluminum alloys and tempers are so tough that brittle or lowductility fracture (i.e., unstable or selfpropagating crack growth in elastically Notched-Bar Impact Testing (Charpy Impact Testing) of Aluminum Alloys The fracture behavior of ferritic steels, specifically, the transition over a relatively narrow range of temperature from a high resistance to fracture to very low resist- For info go to www.aws.org/ad-index 14 APRIL 2012 http://www.aws.org/ad-index

Table of Contents for the Digital Edition of Welding Journal - April 2012

April 2012 - TOC Listing
Unlocking Your Gas Metal Arc Welding Potential - A study sponsored by the National Shipbuilding Research Program investigated low-cost modifications to equipment or parameters that improved welding performance - P. A. Blomquist
Community College Welding Program Update - Many community colleges around the country are equipping future workers with the skills manufacturers need D. Postlethwaite
Modern Power Source Technology Drives Process Improvement - New technology in weld monitoring is making it easier to access the data by all the appropriate personnel and understand how it should be applied to benefit weld quality - T. McEllis
Building a Welding Career from the Ground Up - A thirty-two-year career welder shares her passion for the profession with others in hopes of inspiring them to expand their skills and knowledge
How Today’s Power Sources Aid Pulsed GMAW - The advanced welding machines of today can deliver power to the arc in almost any form and can react with split-second timing to avoid adverse arc phenomena - L. Barley
Fiber Lasers Perform Precision Cutting for Medical Devices - There are many methods to cut thin tubular structures often used in medical devices, but fiber lasers are emerging as the precision machines of choice
Arc Characteristics in Pulsed-GMA Welding with Acute - Groove Angles The characteristics of a joint tracking sensor were monitored under conditions of different groove angles and root openings - R-H. Kim et al.
Design of Experiment and Goal Programming Application for the GMAW Process - This study was conducted to determine critical gas metal arc welding variables and ways to optimize them - Y. T. Iç et al.
Predictive and Measurement Methods for Delta Ferrite Determination in Stainless Steels - The advantages and limitations of predictive measurement methods for δ ferrite are outlined - M. A. Valiente Bermejo
Susceptibility of IN740 to HAZ Liquation Cracking and Ductility-Dip Cracking - Conditions that lead to cracking susceptibility of nickel-based IN740 were simulated to determine an action for its prevention - J. E. Ramirez
Editorial
Washington Watchword
Press Time News
News of the Industry
Aluminum Q&A
Brazing Q&A
Product & Print Spotlight
Coming Events
Certification Schedule
Welding Workbook
Society News
Interpretations D1.1
Guide to AWS Services
Personnel
Welding School Profiles
Classifieds
Advertiser Index

Welding Journal - April 2012