Page 319 - Biaxial Multiaxial Fatigue and Fracture

BiaxiaVMultiaxial Fatigue and Fracture
Andrea Carpinteri, Manuel de Freitas and Andrea Spagnoli (Eds.)
0 Elsevier Science Ltd. and =IS. All rights reserved. 303

INFLUENCE OF DEFECTS ON FATIGUE LIFE OF ALUMINIUM PRESSURE
DIECASTINGS

Fernando Jorge LINO’, Rui Jorge NETO’, Alfred0 OLIVEIRA2 and Fernando Manuel
Fernandes de OLIVEIR4’
‘Faculdade de Engenharia, Universidade do Porto, Departamento de Engenharia Mecknica e
Gestrib Industrial, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
’INEGI, Instituto de Engenharia Mecdnica e GestZo Industrial, Rua do Barroco, 174-214,
4465-591 Leqa do Balio, Porto, Portugal

ABSTRACT

Fatigue life of aluminium pressure diecastings is strongly dependent on the microporosity level
of the parts. Even in a very controlled production process, it is almost impossible to obtain
aluminium parts without micropores, which means that a considerable amount of parts are
rejected, in accordance to internal companies criteria. Although these criteria are based on
standards, they change from company to company, and depend on the type of the parts and the
amount, size and location of the micropores. Many times, parts that could have a good fatigue
life are rejected based on these criteria.
The aim of the present work is to study the influence of the microporosity level and size on the
fatigue life of aluminium pressure diecastings. Two different lots of samples, removed from
aluminium components (considered unacceptable and acceptable) were tested using the
staircase fatigue test. All the fractured parts were analysed macro and microscopically and the
images obtained were digitalized in order to classify the size and amount of the micropores.
The results obtained were compared with the fatigue life curves, in order to evaluate the
influence of the microporosity on the fatigue life of aluminium components.

KEY WORDS

Fatigue life, manufacturing defects, aluminium, staircase fatigue test, diecasting.

INTRODUCTION

One of today’s greatest challenges in the foundry industry is the production of complex and
structurally sound parts. At the forefront of this challenge is the porosity and inclusions size
and levels, and how and where they develop. The presence, even in small levels, of these types
of defects in pressure diecastings can lead to a significant reduction in the tensile strength,
ductility, pressure tightness and fatigue life, affecting the life and the integrity of the cast parts
[I].