6xxx Aluminium Sheet Processing for High Surface Quality
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Solution Overview
Problem
The automotive industry requires a method to produce 6xxx series aluminium sheets with high tensile yield strength, good formability, and high surface quality suitable for cold stamping operations, while also ensuring high corrosion resistance and minimizing surface defects like roping, which current methods are inefficient and costly.
Innovation Solution
A method involving homogenization of ingots with specific alloy compositions, followed by controlled hot rolling and cooling rates to achieve high recrystallization and grain size optimization, combined with cold rolling and solution heat treatment, to produce sheets with improved surface quality and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple heat treatments are applied to improve surface quality and formability, then surface quality and mechanical properties are improved, but production time and cost increase
Solution Approach 1:
The patent combines multiple heat treatment operations (homogenization, solution treatment, and aging) into a single integrated heat treatment process. The ingot undergoes homogenization at 500-580°C followed by direct cooling to room temperature, then hot rolling, and finally solution treatment at 400-500°C with controlled cooling rates (100-500°C/hr). This integration eliminates separate heat treatment steps, reducing production time while maintaining surface quality below 4.8 VDA rating and achieving tensile yield strength ≥200 MPa.
Solution Approach 2:
The patent optimizes specific process parameters to achieve both high surface quality and reduced production time. Key parameter changes include: controlling hot rolling finish temperature at 320-360°C to achieve ≤160 μm grain size; applying controlled cooling rates of 100-500°C/hr during solution treatment; and maintaining specific alloy composition ranges (Si: 0.4-1.5%, Mg: 0.2-1.2%, Mn: 0.03-0.5%, Cr: 0.01-0.4%). These parameter optimizations enable the material to achieve desired properties through fewer process steps.
2Manufacturing precision
If traditional heat treatment methods are used to achieve high surface quality, then roping and paint brush lines are reduced, but the process becomes long and expensive
Solution Approach 1:
The patent applies preliminary homogenization treatment to the ingot before hot rolling, holding it at 500-580°C to ensure uniform composition and eliminate segregations. This preliminary action prevents surface defects like roping and paint brush lines from forming in the first place, eliminating the need for subsequent corrective treatments. The homogenized ingot is then directly cooled and hot rolled, streamlining the process while maintaining high surface quality.
Solution Approach 2:
The patent maintains continuous useful action by transitioning directly from homogenization to hot rolling without intermediate cooling to room temperature or storage steps. The ingot is homogenized at 500-580°C, then cooled at controlled rates (100-500°C/hr) directly to the hot rolling temperature range, and immediately hot rolled. This continuous process eliminates idle time and additional heating cycles, reducing both production time and energy consumption while preventing surface defects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method enhances productivity by achieving high tensile yield strength, formability, and surface quality, while reducing roping and corrosion resistance, with a significant improvement in surface quality and mechanical properties, as demonstrated by the examples provided.
Implementation Method 1
homogenizing the ingot
Implementation Method 2
cooling the homogenized ingot with a cooling rate in a range from 150 °C/h to 2000 °C/h directly to a hot rolling starting temperature HRST... with such conditions that at least 90% recrystallization is obtained
Implementation Method 3
hot rolling the homogenised ingot at a starting hot roll temperature of 450 °C to 480 °C and a finishing hot roll temperature of 320 °C to 360 °C
Implementation Method 4
subjecting the cold rolled sheet to a solution treatment
Data Source
AI summary
The invention concerns a method for producing a 6xxx series aluminium sheet comprising the steps of homogenizing an ingot made from a 6XXX series aluminium alloy; cooling the homogenized ingot with a cooling rate in a range of from150 °C/h to 2000 °C/h directly to the hot rolling starting temperature; hot rolling the ingot to a hot rolling final thickness and coiling at the hot rolling final thickness with such conditions that at least 90%recrystallization is obtained while controlling the temperatures of hot rolling, in particular the relationship between the hot rolling starting temperature and the hot rolling exit temperature and/or controlling the grain size after coiling,; cold rolling to obtain a cold rolled sheet.The method of the invention is particularly helpful to make sheets for the automotive industry which combine high tensile yield strength and good formability properties suitable for cold stamping operations, as well as high surface quality.