Search Results for ZA-27

A die-cast zinc adapter used in a snowthrower failed catastrophically in a brittle overload manner. The component had a chemical composition similar to standard zinc alloy ZA-27 (UNS Z35840), although the iron content was much higher and the copper slightly lower. The mechanical properties and alloy designation were not specified. Investigation (visual inspection, 187x SEM images, unetched 30x images, hardness testing, and chemical analysis) of both the failed adapter and an exemplar casting from known-good lot supported the conclusion that the casting failed as a result of brittle overload fracture due to excessive iron-zinc phase and gross porosity. These conditions acted synergistically to reduce the strength of the material. The composition was nonstandard, and the inherent brittleness suggested that it was unlikely that this material was an intentional proprietary alloy. No recommendations were made.

This article aims to identify and illustrate the types of overload failures, which are categorized as failures due to insufficient material strength and underdesign, failures due to stress concentration and material defects, and failures due to material alteration. It describes the general aspects of fracture modes and mechanisms. The article briefly reviews some mechanistic aspects of ductile and brittle crack propagation, including discussion on mixed-mode cracking. Factors associated with overload failures are discussed, and, where appropriate, preventive steps for reducing the likelihood of overload fractures are included. The article focuses primarily on the contribution of embrittlement to overload failure. The embrittling phenomena are described and differentiated by their causes, effects, and remedial methods, so that failure characteristics can be directly compared during practical failure investigation. The article describes the effects of mechanical loading on a part in service and provides information on laboratory fracture examination.

Overload failures refer to the ductile or brittle fracture of a material when stresses exceed the load-bearing capacity of a material. This article reviews some mechanistic aspects of ductile and brittle crack propagation, including a discussion on mixed-mode cracking, which may also occur when an overload failure is caused by a combination of ductile and brittle cracking mechanisms. It describes the general aspects of fracture modes and mechanisms. The article discusses some of the material, mechanical, and environmental factors that may be involved in determining the root cause of an overload failure. It also presents examples of thermally and environmentally induced embrittlement effects that can alter the overload fracture behavior of metals.