Effects of Pin Geometry and Processing Parameters on Macroscopic Defects in Three-Layer Friction Stir Additive Manufacturing of AA7075

Akbari, Mostafa; Sardarizadeh, Amirhossein; Hassanzadeh, Ezatollah

doi:10.48301/vjtve.2026.607815.1179

Effects of Pin Geometry and Processing Parameters on Macroscopic Defects in Three-Layer Friction Stir Additive Manufacturing of AA7075

Document Type : Original Article

Authors

Mostafa Akbari

Amirhossein Sardarizadeh

Ezatollah Hassanzadeh

Department of Mechanical Engineering, Technical and Vocational University (TVU), Tehran, Iran.

10.48301/vjtve.2026.607815.1179

Abstract

Friction stir additive manufacturing (FSAM) relies on local softening, material transport, and interfacial consolidation to join successive metal sheets. This study examines macroscopic discontinuities and defects in three-layer AA7075 builds produced from nominally 1.6 mm sheets through two joining stages. Twenty selected combinations of conical, cylindrical, and threaded pins, 2 and 3 mm pin lengths, rotational speeds of 2000 and 3150 rpm, and traverse speeds of 36 and 45 mm/min were assessed using cross-sectional photographs. Visible discontinuity areas ranged from 0.08 to 2.09 mm² in the sections containing resolved defects. Sections with no detectable macroscopic discontinuity (ND) were assigned zero for all comparative means. Threaded pins gave the lowest pooled mean discontinuity area, 0.334 mm², and the threaded 2 mm tool at 45 mm/min produced ND sections at both rotational speeds. Comparisons at otherwise identical settings showed that changing traverse speed, rotation, or pin length could improve or impair consolidation depending on the accompanying tool geometry. These responses are interpreted in terms of geometry-dependent stirring, interlayer engagement, and the balance between thermal softening and material containment. The results identify favorable tested combinations and indicate that pin profile and processing speeds should be selected together to promote interlayer filling and closure.

Keywords

Friction stir additive manufacturing

AA7075

Pin geometry

Pin length

Subjects