Analyse des défauts de pliage et d'inclusion dans 5052 Cercles en aluminium laminés à chaud
This document provides a systematic analysis of two typical defects in 5052 hot-rolled aluminum circles—Folding/Lapet Inclusion—covering characteristics, causes, détection, and prevention. These defects directly impact stamping, emboutissage profond, qualité de surface, et propriétés mécaniques, making them key focuses in production and quality control.
1. Folding Defect (Folding/Lap)
1️⃣ Characteristics
- Macroscopic: Tongue-shaped, linear, or layered overlapping patterns on the surface, aligned with the rolling direction. Edges are often rounded, and severe cases may show cracking.
- Microscopic: Oxidation, decarburization/dealloying at the fold. Material flow lines are cut, local microstructure is disturbed, creating stress concentration points.
- Typical Locations: Edges, corners, areas of severe deformation, or regions extending from original ingot defects.
2️⃣ Root Causes
- Ingot/Billet Defects: Surface cracks, subsurface blowholes, segregation bands, unfilled flash/burrs from casting, which are pressed into the material during rolling.
- Improper Hot Rolling Process:
- Non-uniform heating and large temperature gradients cause uneven metal flow and local metal accumulation.
- Excessive reduction per pass or deformation ratios cause edge metal backflow and folding.
- Poor roll shape/guide setup, or roll surface spalling leads to local over-compression and metal entrapment.
- Circle Forming/Trimming Issues: Shearing burrs or tears during cutting, which develop into folds during subsequent rolling/annealing; excessively sharp corners hindering metal flow.
- Material Influence (5052): Higher Mg content results in slightly lower plasticity compared to pure aluminum, increasing the tendency for folding and micro-cracking under uneven deformation.
3️⃣ Detrimental Effects
- Destroys metallic continuity, reducing tensile strength, limite d'élasticité, et allongement.
- Causes cracking or wrinkling during stamping/deep drawing; leads to black lines or color differences after surface treatment.
- Acts as a fatigue crack initiation site, significantly reducing service life.
2. Inclusion Defect (Inclusion)
1️⃣ Characteristics
- Macroscopic: Spot, stringer, or block-shaped dark/bright foreign objects on/near the surface, often elongated into lines or bands along the rolling direction.
- Microscopic: Primarily non-metallic inclusions (par ex., Al₂O₃, MgO, refractory materials, refining slag, external contaminants). They disrupt matrix continuity and often initiate micro-cracks and stress concentration in surrounding areas.
- Types: Endogenous(formed during melting/casting) et exogenous(introduced from furnace lining, tools, environment).
2️⃣ Root Causes
- Fusion & Processus de coulée (Primary Source):
- Dirty raw materials (aluminum/magnesium ingots) with excessive oxide skins.
- Inadequate melt purification, insufficient degassing and slag removal.
- Damaged or eroded furnace lining, troughs, or filtration systems contaminating the melt.
- Casting-level fluctuations, slag entrapment, or failed filtration.
- Laminage à chaud & Downstream Processes:
- Incomplete removal of furnace scale, leading to rolled-in oxide inclusions.
- Wear debris from rolls, guides, or cutting tools contaminating the metal.
- Environmental dust, graisse, or other foreign matter being pressed into the surface.
- Material Influence (5052): Mg is prone to oxidation, forming hard-to-remove MgO·Al₂O₃ spinel inclusions, easily forming banded defects.
3️⃣ Detrimental Effects
- Severely reduces plasticity, toughness, and fatigue strength, with transverse properties more significantly affected.
- Causes cracking or delamination during stamping; leads to black spots, trous d'épingle, or pitting after surface treatment.
- Increases scrap rates and rework costs.
3. Detection Methods
- Visuel & Macroscopic Examination: For surface folds and obvious inclusions; clearer after acid/alkali etching.
- Tests par ultrasons (Utah): Detects internal inclusions, delamination, and folds.
- Eddy Current Testing (ET): Rapid screening for surface/near-surface defects.
- Analyse métallographique: Determines inclusion type, taille, distribution, and fold characteristics (oxide layer, microstructure).
- Tests mécaniques: Tensile and bend tests to verify the impact of defects on properties.
4. Prevention & Control Measures (Full Process)
1️⃣ Melting & Fonderie (Contrôle des sources)
- Strictly control raw material purity; use high-quality remelt ingots; store Mg ingots under protective atmosphere or sealed.
- Optimize melting practice: Melt at lower temperatures, stir adequately, employer online degassing (par ex., SNIF/Alpur) + multi-stage filtration (par ex., 30ppp + 50ppp).
- Stabilize casting parameters: Low metal level, slow casting speed, strong cooling to reduce slag entrapment and porosity.
- Apply ingot homogenization and scalping to thoroughly remove oxide layers, segregation zones, and subsurface defects.
2️⃣ Hot Rolling & Circle Forming
- Ensure ingots are heated uniformly and thoroughly, maintaining consistent temperature without overheating.
- Design合理的道次压下 rational pass reduction schedules, control total deformation, and avoid edge backflow and metal accumulation.
- Optimize roll profiles and guide systems; promptly repair roll surface damage.
- Employ burr-free shearing or laser cutting for blanking; control corner radii to prevent tearing.
- Maintain clean production throughout to prevent contamination by scale, poussière, or tool debris.
3️⃣ Specific Optimizations for 5052 Alliage
- Appropriately increase hot rolling temperature (par ex., 420–480°C) to improve plasticity and flow uniformity.
- Control Mg content towards the mid-lower limit of the specification to reduce oxide inclusion formation.
- Introduce intermediate annealing when necessary to relieve work hardening and internal stress, reducing the risk of folding and cracking.
5. Quick Assessment & Disposition Guidelines
- Folding: Visible overlapping patterns with oxidation tint and cracking tendency → Typically classified as non-conforming. Nécessite scalping/grinding or scrapping.
- Inclusions: Foreign object spots/strings on surface or internally → Rate according to relevant normes. Material exceeding limits should be scrapped or downgraded.
Note: The above is based on the characteristics of 5052 aluminum alloy and common defects in hot-rolled circles. Actual production should apply these guidelines flexibly in conjunction with specific processes and standards.