A method for multi-pulse laser shock peening gradient strengthening of a guide rail aluminum alloy bending site

Abstract

The application discloses a kind of gradient strengthening methods of rail aluminum alloy bending site of multi-pulse laser impact, and gradient residual compressive stress layer is formed in bending area by layering control laser parameter.Specific steps include: (1) pretreatment: after ultrasonic cleaning, coating absorption layer and constraint layer;(2) gradient strengthening: surface layer uses low energy (2-3J), small spot (3-4mm), middle layer is promoted to 4-6J, deep layer uses high energy (6-8J), large spot (5-6mm), with 60%-90% coverage and 2-8 times pulse realizes stress gradient control;(3) optimization scanning path: using contour line+0° / 90° bidirectional cross scanning ensures uniformity;(4) post-processing: stress distribution is detected by XRD and performance is tested.The method makes the fatigue life of aluminum alloy bending site increase by 2-4 times, and the friction coefficient reduces by 20%-40%, and is especially suitable for strengthening of curved surface component such as automobile sunroof rail.

Description

Technical Field

[0001] This invention relates to the field of laser processing and material surface strengthening technology, specifically to a gradient strengthening method for the surface of aluminum alloy guide rails based on multi-pulse laser shock strengthening. In particular, it proposes a unique gradient strengthening technology for the complex stress distribution and wear resistance requirements of aluminum alloy guide rails for sunroofs. Background Technology

[0002] Automotive sunroof guide rails are typically made of 6063 or 6061 aluminum alloy. The bending sections are critical areas of stress concentration, making them prone to failure due to fatigue and frictional wear during long-term use. Currently, traditional surface treatment methods (such as anodizing and shot peening) suffer from limited strengthening depth, uneven stress distribution, and compromised surface integrity, making them unsuitable for the demands of high-performance automotive sunroofs.

[0003] Laser shock peening (LSP), as a non-contact, high-energy-density strengthening technique, can induce plasma shock waves through laser pulses to form deep residual compressive stress on the surface and inside of materials, effectively improving fatigue resistance. However, LSP treatment for the curved parts of automotive sunroof guide rails still has the following problems:

[0004] 1. Insufficient stress gradient optimization: A single laser shock parameter may result in an excessively shallow or uneven strengthening layer, making it difficult to adapt to the complex stress distribution in bending areas.

[0005] 2. Inappropriate reinforcement path: Traditional LSP processing paths are mainly for planar or simple curved surfaces. The reinforcement path for curved parts lacks optimization, which may lead to uneven reinforcement or local damage.

[0006] Therefore, this invention proposes a gradient strengthening method based on multi-pulse LSP, which forms an optimized strengthening gradient in the bending part of aluminum alloy by adjusting the laser energy, coverage, number of pulses and scanning path layer by layer, thereby improving fatigue life and wear resistance. Summary of the Invention

[0007] This invention aims to provide a multi-pulse laser shock gradient strengthening method for the bent parts of aluminum alloy guide rails. By gradually adjusting the laser shock energy and scanning path, gradient residual compressive stress is introduced into the material surface and interior, optimizing the mechanical properties of the bent parts and achieving depth optimization and uniform distribution of the strengthening layer. The specific steps are as follows: (1) Pretreatment

[0008] Select 6061 or 6063-T6 aluminum alloy samples (thickness 3-5mm), and perform ultrasonic cleaning on the bent parts to remove oil and impurities.

[0009] Apply an absorption layer (black tape or metallic coating) to the curved area and apply a restraint layer (1mm water film) to enhance the laser shock effect.

[0010] (2) Multi-pulse gradient laser shock enhancement

[0011] Using an Nd:YAG laser (wavelength 1064nm), LSP processing was performed according to a gradient optimization strategy:

[0012]

[0013] First stage (surface strengthening): Using low energy (2-3J) and a small spot diameter (3-4mm), the bending area is uniformly covered to form a preliminary residual compressive stress layer, thereby improving wear resistance.

[0014] Second stage (mid-layer reinforcement): Gradually increase energy (4-6J) and coverage (70-80%), increase the number of pulses, and enhance the thickness of the reinforcement layer.

[0015] The third stage (deep strengthening): High energy (6-8J) and larger spot size (5-6mm) are used in the stress concentration area of ​​the bending part, and the number of pulses is increased (5-8 times) to form deeper residual compressive stress and enhance fatigue resistance.

[0016] (3) Enhance path optimization

[0017] A curved contour scanning path is used to ensure that the laser impact is evenly distributed in the curved area, preventing stress concentration.

[0018] A bidirectional cross-scanning method (0° / 90° cross) is adopted to enhance stress uniformity and reduce local stress concentration.

[0019] (4) Post-processing

[0020] XRD (X-ray diffraction) was used to test the residual stress distribution after strengthening to ensure optimized stress gradient. The advantages of this invention are:

[0021] a) Gradient strengthening design: Utilizing multi-level laser shock parameters, different depths of strengthening gradients are achieved to improve fatigue strength and wear resistance. Through surface strengthening and nano-hardening effects, the coefficient of friction is reduced by 20-40%.

[0022] b) Multi-pulse laser shock spectroscopy: Utilizing a combination of high and low energy pulses, surface refinement and strengthening, as well as deep residual stress optimization, are achieved. Compared to untreated samples, multi-pulse LSP treatment can improve the fatigue life of bending sections by 2-4 times.

[0023] c) Optimize the impact path: adopt a non-uniform scanning path to improve the uniformity of strengthening and avoid stress concentration. Attached Figure Description

[0024] Figure 1Diagram of bending section of multi-pulse laser shock peening strengthened aluminum alloy

[0025] Figure 2 Contour line scan diagram Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the invention:

[0027] Example 1: Low-energy, high-coverage multi-pulse gradient enhancement strategy

[0028] Step 1: Sample preparation

[0029] 6063-T6 aluminum alloy (3mm thick) was selected, and the bent parts were ultrasonically cleaned to remove the surface oxide layer and oil stains. Then, a black adhesive tape absorbent layer was applied, and a 1mm thick water film was placed on top as a restraining layer.

[0030] Step 2: Setting Laser Shock Enhancement Parameters

[0031] LSP processing was performed using an Nd:YAG laser (wavelength 1064nm, pulse width 30ns) as follows:

[0032]

[0033] Step 3: Enhance path optimization

[0034] Contour scanning + cross scanning (0° / 90°) is used to ensure uniform enhancement distribution.

[0035] Step 4: Performance Testing

[0036] Perform XRD testing.

[0037] Example 2: High-energy, low-coverage single-layer reinforcement strategy

[0038] Step 1: Sample preparation

[0039] 6061-T6 aluminum alloy (4mm thick) is used. After mechanical polishing of the bent parts, a nano carbon black absorption layer is coated and a 1mm thick water film is applied as a constraint layer.

[0040] Step 2: Setting Laser Shock Enhancement Parameters

[0041]

[0042] Step 3: Enhance path optimization

[0043] The contour line scanning path is used to expand outward from the center of the curved area to improve the uniformity of reinforcement.

[0044] Step 4: Performance Testing

[0045] Perform XRD testing.

[0046] Example 3: Composite Energy Partition Gradient Enhancement Strategy

[0047] Step 1: Sample preparation

[0048] 6063-T5 aluminum alloy (3.5mm thick) was selected. A black tape absorption layer was used on the outside of the bend, and a nano carbon black absorption layer was used on the inside of the bend. A 1mm thick water film was also used as a constraint layer.

[0049] Step 2: Setting Laser Shock Enhancement Parameters

[0050] Set enhancement parameters for different regions:

[0051]

[0052] Step 3: Enhance path optimization

[0053] By employing a regional zoning scanning path, impact energy is increased on the outer (tension zone) area to enhance crack resistance.

[0054] Bidirectional cross-scanning (0° / 90°) is used to improve overall uniformity.

[0055] Step 4: Performance Testing

[0056] Perform XRD testing.

Claims

1. A method for multi-pulse laser shock gradient strengthening of the bent portion of an aluminum alloy guide rail, characterized in that, Includes the following steps: Step 1: Preprocessing 1) Select 6061 or 6063-T6 aluminum alloy samples (thickness 3-5mm) and perform ultrasonic cleaning on the bent parts to remove oil and impurities. 2) Apply an absorption layer (black tape or metal coating) to the curved area and apply a restraint layer (1mm water film) to enhance the laser shock effect. Step 2: Multi-pulse gradient laser shock enhancement 1) Using an Nd:YAG laser (wavelength 1064nm), LSP processing was performed according to a gradient optimization strategy. 2) Enhance path optimization. Step 3: Post-processing XRD (X-ray diffraction) was used to test the residual stress distribution after strengthening to ensure stress gradient optimization.

2. The method according to claim 1, wherein the surface reinforcement uses a low-energy impact of 2-3J, the middle layer reinforcement uses 4-6J, and the deep layer reinforcement uses 6-8J, and the coverage (60%-90%) and the number of pulses (2-8 times) are optimized to achieve a gradually increasing reinforcement effect.

3. The method according to claim 1, wherein the laser scanning path adopts contour line scanning + bidirectional cross scanning to optimize stress distribution.

4. The method according to claim 1, wherein the coverage of the enhanced area is gradually increased from 60% to 90%.

5. The method according to claim 1, wherein the depth of the reinforcing layer at the bending portion can reach more than 600 μm.

6. The method according to claim 1, wherein the laser pulse width is set in the range of 20-30 ns.

7. The method according to claim 1, wherein XRD residual stress testing is performed after strengthening to ensure stress gradient optimization.

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