Asymmetrical precipitation on {10-12} twin boundary in magnesium alloy

TL;DR

This study investigates how {10-12} twin boundaries in magnesium alloys influence beta-Mg17Al12 precipitation, revealing asymmetrical precipitate shapes, orientation relationships, and proposing a new variant selection rule.

Contribution

It uncovers the unique asymmetric precipitation behavior on {10-12} twin boundaries and introduces a new variant selection rule specific to magnesium alloys.

Findings

Precipitates on twin boundaries are rod-like, while others are lath-shaped.

Precipitates maintain OR only with twin or matrix, not both.

Certain precipitate variants are absent, leading to a new variant selection rule.

Abstract

Precipitation on deformation defects is essential for enhancing mechanical properties of age-hardenable alloys. {10-12} twinning is common in deformed alloys with hexagonal-close-packed structure. In this work, we revealed how {10-12} twin boundary (TB) influences beta-Mg17Al12 precipitation in Mg-9Al-1Zn alloy. The precipitates on the TB are rod-like, while others are lath-shape. The precipitates hold the Burgers orientation relationship (OR) only with twin or matrix, contrary to traditional wisdom in others alloys that precipitates on TB symmetrically keep an OR with both twin and matrix. Moreover, certain precipitate variants are absent, and a new rule for variant selection on TB is proposed.