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The microstructure, mechanical properties and fatigue crack propagation (FCP) of extruded magnesium alloy AM60 were investigated and compared with rolled AM60. The extruded AM60 has an inhomogeneous microstructure characterized by alpha-matrix, beta phases and Al-Mn precipitates and denuded zones as well, whereas rolled AM60 has fine grains. The change in strain-hardening exponent of extruded AM60 with strain rate is ascribed to inhomogeneous microstructure. In situ double twinning: (10 (1) over bar2) - (01 (1) over bar2) and {10 (1) over bar1} - {10 (1) over bar2} occurred during FCP of extruded alloy. Its crack initiation and growth are related to slip bands, double twinning and intermetallic compounds. Small cracks resulted from oxide and intermetallic compounds in rolled AM60 may be responsible for oscillatory crack growth and crack arrest. Extruded AM60 has a slower FCP rate than rolled one. (C) 2009 Elsevier Ltd. All rights reserved.