GB/T 3246.1-2024 Inspection method for structure of wrought aluminium and aluminium alloy products - Part 1: Inspection method for microstructure
1 Scope
This document describes a method for the microstructure of wrought aluminium and aluminium alloy products.
This document is applicable to the microstructure inspection for wrought aluminium and aluminium alloy ingots for casting (or ingot blanks), plates and strips, foils, tubes, rods, molds, wires, forgings and other processed products by using optical (metallographic) microscopes, scanning electron microscopes, transmission electron microscopes and other instruments.
2 Normative references
The following documents contain requirements which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 6682 Water for analytical laboratory use - Specification and test methods
GB/T 8005.1 Aluminium and aluminium alloy - Terms and definitions - Part 1: Product and method of processing and treatment
GB/T 8170 Rules of rounding off for numerical values & expression and judgment of limiting values
JJF 1914 Calibration Specification for Metallurgical Microscopes
YS/T 1623 Inspection of aging precipitates for aluminium alloys — Transmission electron microscopy method
YS/T 1624 Evaluation method of homogenized effect for aluminium alloy ingots
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 8005.1 and the following apply.
3.1
eutectic melting
phenomenon in which the temperature of a metal reaches or exceeds the melting point or solid-phase line of a low-melting-point eutectic in an alloy, resulting in remelting of the eutectic or solid-solution grain boundaries of the metal
Note: The difference between eutectic melting microstructure and normal microstructure is shown in Figure 1.
a) Normal structure b) Eutectic melting structure
Key:
1——Remelting eutectic sphere;
2——Local remelting and widening of grain boundaries;
3——Remelting triangle.
Figure 1 Microstructure diagram of normal structure and eutectic melting structure of 7055T4 plate (etched with No. 6 etchant)
3.2
heat treat induced porosity
air holes appearing on the surface of wrought aluminium and aluminium alloy materials blistering or near the surface along the grain boundaries after heat treatment due to high humidity in the air inside the furnace (due to the moisture contained in the furnace body itself, the oil stains on the surface of the product or the cooling medium brought into the furnace during the solution treatment process, etc.) when treating aluminium alloy materials at higher temperatures
Note: Heat treat induced porosity are also called high temperature oxidation (HTO), and the typical microstructure characteristics are shown in Figure 2.
Figure 2 Diagram of heat treat induced porosity produced by heat treatment of 2A12T4 bar (etching with No. 6 etchant)
3.3
cladding layer
layer of aluminium or aluminium alloy coated on the surface of a wrought aluminium alloy plate in order to improve corrosion resistance or certain technological performance
Note: If the cladding layer is pure aluminium, it is also called aluminium cladding. The cladding layer is shown in Figure 3 and Figure 4.
Figure 3 Diagram of microstructure of 2A12T4 sheet and plate covered with aluminium layer (etched with No. 6 etchant)
Figure 4 Diagram of microstructure of 2Q515 composite sheet and plate cladding layer (crazing layer) (etching with etchant No. 6)
3.4
copper diffusion
phenomenon that aluminium-copper-magnesium alloy aluminium-clad sheet and plate is heated at high temperature for a long time, so that copper atoms in the alloy diffuse to the aluminium clad layer along the grain boundary
Note: the typical microstructure of copper diffusion is shown in Figure 5.
Foreword i
Introduction iii
1 Scope
2 Normative references
3 Terms and definitions
4 Optical (metallographic) microscopy
5 Scanning electron microscopy
6 Transmission electron microscopy
7 Expression of results
8 Test report
Annex A (Informative) Typical microstructures of wrought aluminium and aluminium alloy products
Annex B (Normative) Determination of grain size
Annex C (Normative) Determination of size of secondary phases and particulate matters
Bibliography
